Thermal transfer sheet, coating liquid for colorant layer, method for manufacturing thermal transfer sheet, and image forming method

ABSTRACT

The purpose of the present invention is to provide a thermal transfer sheet which can prevent a kick and a scumming, and can form a photographic tone color image of high quality with a continuous tone image by sublimation transfer, while expanding the range of choices for colorants to be included in a colorant layer; a coating liquid for colorant layer to be used for forming the colorant layer of this thermal transfer sheet; a method for manufacturing this thermal transfer sheet; and image forming method employing this thermal transfer sheet. The problem is solved by a thermal transfer sheet ( 1 ) in which at least a colorant layer ( 3 ) is layered on a substrate sheet ( 2 ), wherein the colorant layer ( 3 ) contains a predetermined solvent, a colorant ( 10   x ) dispersible in the predetermined solvent, a dispersant, and a binder resin, and the dispersant being one or more selected from the group consisting of polyether-based dispersants, graft type polymer dispersants, acryl-based block type polymer dispersants, urethane-based polymer dispersants and azo-based dispersants.

TECHNICAL FIELD

The present invention relates to a thermal transfer sheet, a coatingliquid for colorant layer, a method for manufacturing thermal transfersheet and an image forming method.

BACKGROUND TECHNIQUE

Conventionally, thermal transfer method has been widely used as a simpleprinting method. The melt-transfer method as one of the thermal transfermethod is an image forming method wherein a thermal transfer sheet,which has a thermally fusible ink layer comprising a colorant, such as apigment, and a binder such as a thermally fusible wax or resin, issuperposed on a thermal transfer image-receiving sheet such as a paperor a plastic film; then, an energy in accordance with image informationis applied from the back side of the thermal transfer sheet by a heatingmeans such as a thermal head; and thereby the colorant is transferredonto the thermal transfer image-receiving sheet together with thebinder. The image formed by the melt-transfer method is suitable forrecording binary images such as characters, since the image hasexcellent sharpness and high concentration.

On the other hand, the sublimation transfer method as another one of thethermal transfer method is another image forming method wherein athermal transfer sheet, which has a colorant layer comprising a dyewhich is able to be transferred thermally by sublimation, is superposedon a thermal transfer image-receiving sheet in which a dye receivinglayer is provided on a substrate, then, an energy in accordance withimage information is applied from the back side of the thermal transfersheet by a heating means such as a thermal head; and thereby only thesublimable dye is transferred onto the thermal transfer image-receivingsheet. With respect to the sublimation transfer method, since thetransferring amount of dye can be controlled by the amount of energyapplied, it is possible to form a gray-scale image in which imagedensity is controlled. In addition, since the colorants used are dyes,the image formed has transparency. Thus, when dyes of different colorsare superposed, the reproducibility of neutral tints becomes excellent.Therefore, when using thermal transfer sheets of different colors suchas yellow, magenta, cyan, black or the like, and transferring dye ofeach color on the thermal transfer image-receiving sheet so as tosuperpose the dyes each other, it is possible to form a photographicfull-color image of high quality in which reproducibility of neutraltints is excellent. Furthermore, since the sublimation transfer methodcan express the full color image as the original onto the thermaltransfer image-receiving sheet clearly, it is applied to a color imageforming for a digital camera, a video camera, a computer or the like.The image is one that is high-quality comparable to silver halidephotography.

In general, the thermal transfer sheet is stored and used in woundstate. When the colorant contained in the colorant layer is present in astate of being localized to the surface of the colorant layer bybleeding, etc., the sublimable dye tends to migrate to the back facelayer side of the thermal transfer sheet (so-called “kick”). When thesublimable dye migrated to the back layer side is again re-migrated tothe colorant layer side (so-called “back”), in particular, in the casethat, in the thermal transfer sheet in which a plural numbers ofcolorant layers which are different in the hue from each other areprovided so as to be layered in parallel on the substrate sheet acrossthe surface of the substrate sheet, as being frame sequentially, thesublimable dye migrated to the back layer side is again re-migrated toanother colorant layer which is different in the hue from the sublimabledye, a decrease in color development property would be caused at thetime of image formation using the another colorant layer.

Under these circumstances, with respect to the thermal transfer sheetcapable of suppressing the occurrence of kick, various studies have beenmade. For example, in Patent literature 2, a thermal transfer sheetwhich comprises a dye layer provided on one surface of the substratesheet, and a back face layer provided on another surface of thesubstrate sheet, wherein the dye layer contains an indoaniline baseddye, a polyvinyl acetal resin A, and a polyvinyl acetal resin B(represented by the formula (1) in Patent literature 2), has beenproposed. Further, in Patent literature 3, a thermal transfer sheetwhich comprises a dye layer provided on one surface of the substratesheet film and containing a resin and a dye, and a back face layerprovided on another surface of the substrate sheet and containing alubricant and a resin, wherein the dye layer contains a prescribed dye(the dye represented by the formula (1) in Patent literature 3) in aprescribed amount range, has been proposed. According to the thermaltransfer sheets proposed by Patent literatures 2 and 3, it is statedthat it is possible to prevent the migration of colorant to the backlayer side during the storage of the thermal transfer sheet.

Further, in the thermal transfer sheet proposed in Patent Literature 2,since the kind of the dye contained in the dye layer, and the kind ofthe binder resin are limited to the prescribed components, a problemsuch that the width of the material selection becomes narrower isinherent.

PRIOR ART LITERATURE Patent Literature

-   Patent literature 1: JP 2007-119762 A-   Patent literature 2: JP 2009-286060 A-   Patent literature 3: JP 2010-83003 A

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

The present invention has been made in view of such circumstances, andthe present invention aims principally to provide a thermal transfersheet which can prevent a kick and a scumming, and can form aphotographic tone color image of high quality with a continuous toneimage by sublimation transfer, while expanding the range of choices forcolorants to be included in a colorant layer; a coating liquid forcolorant layer to be used for forming the colorant layer of this thermaltransfer sheet; a method for manufacturing this thermal transfer sheet;and image forming method employing this thermal transfer sheet.

Means for Solving the Problems

An aspect of the present invention for solving the above-mentionedproblems is thermal transfer sheet which comprises a substrate and acolorant layer provided on one surface of the substrate sheet, whereinthe colorant layer contains a predetermined solvent, a colorantdispersible in the predetermined solvent, a dispersant and a binderresin, and wherein the dispersant is one or more kinds of dispersantsselected from the group consisting of polyether-based dispersants, grafttype polymer dispersants, acryl-based block type polymer dispersants,urethane-based polymer dispersants and azo-based dispersants.

Further, the colorant layer may contain a quinophthalone-based colorantrepresented by the following formula 1 as a colorant dispersible in thepredetermined solvent:

Wherein, X represents a hydrogen atom or a halogen atom, R¹ represents ahydrogen atom, an alkyl group or derivative thereof having 1 to 5 carbonatoms, an acyl group including an alkyl group or a benzoic ring andhaving a total carbon number of 6 to 10.

In addition, the colorant layer may further contain a colorantrepresented by the following formula 2 as a colorant dispersible to thepredetermined solvent:

wherein, each of R¹-R⁵ represents independently a hydrogen atom, or asulfonated derivative having at least one sulfonic acid group (—SO₃H) orsulfonamide group.

Another aspect of the present invention for solving the above-mentionedproblems is a coating liquid for colorant layer to be used for forming acolorant layer of a thermal transfer sheet, wherein the coating liquidfor colorant layer contains a predetermined solvent, a colorantdispersible in the predetermined solvent, a dispersant and a binderresin; wherein the colorant dispersible in the predetermined solvent isdispersed in a particle size of not less than 50 nm and not more than300 nm in the coating liquid for colorant layer; and, wherein thedispersant is one or more kinds of dispersants selected from the groupconsisting of polyether-based dispersants, graft type polymerdispersants, acryl-based block type polymer dispersants, urethane-basedpolymer dispersants and azo-based dispersants.

In addition, the coating liquid for the colorant layer in the aboveinvention may further contain a quinophthalone-based colorantrepresented by the above formula 1 as a colorant dispersible to thepredetermined solvent.

Still another aspect of the present invention for solving theabove-mentioned problems is a method of manufacturing a thermal transfersheet, which comprises a colorant layer forming step where a coatingliquid for colorant layer is applied onto a surface of a substrate sheetto form a colorant layer; wherein the coating liquid for colorant layerused in the colorant layer forming step contains a predeterminedsolvent, a colorant dispersible in the predetermined solvent, adispersant and a binder resin; wherein the dispersant is one or morekinds of dispersants selected from the group consisting ofpolyether-based dispersants, graft type polymer dispersants, acryl-basedblock type polymer dispersants, urethane-based polymer dispersants andazo-based dispersants.

In addition, the coating liquid for colorant layer may further contain aquinophthalone-based colorant represented by the above formula 1 as acolorant dispersible to the predetermined solvent.

Further, another aspect of the present invention for solving theabove-mentioned problems is an image forming method for forming image ona thermal transfer image-receiving sheet by using a thermal transfersheet having a colorant layer on a surface of a substrate sheet incombination with the thermal transfer image-receiving sheet having areceiving layer on a surface of another substrate sheet, wherein thecolorant layer of the thermal transfer sheet contains a predeterminedsolvent, a colorant dispersible in the predetermined solvent, adispersant and a binder resin; and wherein the dispersant is one or morekinds of dispersants selected from the group consisting ofpolyether-based dispersants, graft type polymer dispersants, acryl-basedblock type polymer dispersants, urethane-based polymer dispersants andazo-based dispersants.

Also, the colorant layer may further contain a quinophthalone-basedcolorant represented by the above formula 1 as a colorant dispersible tothe predetermined solvent.

Furthermore, another aspect of the present invention for solving theabove-mentioned problems is a thermal transfer sheet which comprises asubstrate and a colorant layer provided on one surface of the substratesheet, wherein the colorant layer contains a predetermined solvent, asublimable dye soluble in the predetermined solvent, a colorantdispersible in the predetermined solvent, and a binder resin.

Further, still another aspect of the present invention for solving theabove-mentioned problems is a thermal transfer sheet which comprises asubstrate and a colorant layer provided on one surface of the substratesheet, wherein the colorant layer comprises a layered structure in whicha first colorant layer and a second colorant layer are layered in thisorder; wherein the first colorant layer contains a first solvent, asublimable dye soluble in the first solvent, and a first binder resin;and wherein the second colorant layer contains a second solvent, acolorant dispersible in the second solvent, and a second binder resin.

Further another aspect of the present invention for solving theabove-mentioned problems is a method of manufacturing a thermal transfersheet, which comprises a colorant layer forming step where a coatingliquid for colorant layer is applied onto a surface of a substrate sheetto form a colorant layer; wherein the coating liquid for colorant layercontains a predetermined solvent, a sublimable dye soluble in thepredetermined solvent, a colorant dispersible in the predeterminedsolvent, and a binder resin.

Further, the coating liquid for colorant layer may further contain adispersant.

Furthermore, another aspect of the present invention for solving theabove-mentioned problems is a method of manufacturing a thermal transfersheet, which comprises a first colorant layer forming step where acoating liquid which contains a first solvent, a sublimable dye solublein the first solvent and a first binder resin is applied onto a surfaceof a substrate sheet to form a first colorant layer; and a secondcolorant layer forming step where a coating liquid which contains asecond solvent, a colorant dispersible in the second solvent and asecond binder resin is applied onto the first colorant layer to form asecond colorant layer.

Effect of the Invention

According to the thermal transfer sheet of the present invention, whileexpanding the range of choices for the colorant to be included in thecolorant layer, in other words, without receiving any particularrestrictions on the dye to be contained in the colorant layer, it ispossible to prevent the kick and the scumming. Further, according to thecoating liquid for colorant layer of the present invention, it ispossible to attain a high colorant dispersibility, to improvecoatability and thus, to form the colorant layer of a thermal transfersheet having the above characteristics. Also, according to themanufacturing method of the thermal transfer sheet of the presentinvention, it is possible to manufacture a thermal transfer sheet whichexhibits the above effects. According to the image forming method of thepresent invention, it is possible to form a high-quality photographiccolor image with gradation image by the sublimation transfer.

According to an embodiment of the thermal transfer sheet of the presentinvention, in addition to the above effects, it is possible to enhancethe durability such as light resistance of the printed article, andpossible to repress lowering of the printing density at the highlightportion, and thus, it is possible to form a high-quality photographiccolor image with gradation image by a sublimation transfer. Also,according to the thermal transfer sheet of the other embodiments, inaddition to the above effects, it is possible to forma high densityimage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view showing an example of the thermaltransfer sheet of the first embodiment.

FIG. 2 is a schematic sectional view showing an example of a thermaltransfer sheet of the first embodiment.

FIG. 3 is a schematic sectional view showing an example of theintermediate transfer medium for comparison.

FIG. 4 is a schematic sectional view showing an example of a thermaltransfer sheet of the second embodiment.

FIG. 5 is a schematic sectional view showing an example of a thermaltransfer sheet of the third embodiment.

MODES FOR CARRYING OUT THE INVENTION <<Thermal Transfer Sheet of FirstEmbodiment>>

As shown in FIG. 1, the thermal transfer sheet 1 of the first embodimentaccording to the present invention may takes a configuration in which aprimer layer 4 and a colorant layer 3 are provided in this order on onesurface of a substrate 2, and a back face layer 5 is provided on anothersurface of the substrate. Incidentally, the primer layer 4, and the backlayer 5 are optional components of the thermal transfer sheet of thefirst embodiment. Here, FIG. 1 is a schematic sectional view showing anexample of a thermal transfer sheet of the first embodiment.

Hereinafter, each layer constituting the thermal transfer sheet 1 of thefirst embodiment will be described in detail.

(Substrate Sheet)

The substrate sheet 2 which constitutes the thermal transfer sheet ofthe first embodiment is provided for the purpose of supporting thecolorant layer 3 as mentioned below, or the primer layer 2 and/or theback face layer which may be optionally provided, and it is possible touse any known material for the substrate. Concretely, as the substrate1, any known material may be used as long as it has a known certaindegree of heat resistance and a known certain degree of strength, and,it is possible to select one arbitrarily from materials known in theart. As such a substrate, for instance, a resin film, such aspolyethylene terephthalate film, 1,4-polycyclohexylene dimethyleneterephthalate film, polyethylene naphthalate film, polyphenylene sulfidefilm, polystyrene film, polypropylene film, polysulfone film, aramidefilm, polycarbonate film, polyvinyl alcohol film, cellulose derivativessuch as cellophane and cellulose acetate, polyethylene film, polyvinylchloride film, nylon film, polyimide film, ionomer film, etc.; and apaper such as condenser paper, paraffin paper, synthetic paper, etc.;and a complex such as complex of paper or nonwoven fabric and resin,etc., can be enumerated. Further, although these materials may be usedsingly, it is also possible to use a certain material as a layered filmin which the material is combined with one or more of other materials.

Although there is no particular limitation on the thickness of thesubstrate sheet 2, the thickness of the substrate is not particularlylimited, it is usually about 0.5 μm-50 μm, and preferably, about 3 μm-10μm. The substrate may undergo adhesive treatment on its one or bothsurface, if necessary. By applying the adhesive treatment, it ispossible to improve wettability and/or adhesiveness of a coating liquidfor colorant layer against the substrate sheet on the formation of thecolorant layer by coating the coating liquid for colorant layer to thesubstrate sheet. As the adhesive treatment, it is possible to apply anyresin surface reforming technique known in the art, as-is, such ascorona discharge treatment, flame treatment, ozone treatment,ultraviolet ray treatment, radiation treatment, roughening treatment,chemical agent's treatment, plasma treatment, low-temperature plasmatreatment, primer treatment, grafting treatment, etc., in order to givean ease-adhesive property. These treatments may be applied singly or incombination of two or more kinds of them. In addition, in the case thata plastic film is manufactured via a stretching procedure, the primertreatment mentioned above may be also carried out by coating a primerliquid to an unstretched film and stretching the film thereafter.

(Primer Layer)

As an adhesive treatment of the substrate sheet, a primer layer 4 may beprovided on the substrate sheet. When the primer layer is provided, itbecomes possible to improve the adhesion between the substrate sheet 2and the colorant layer 3, and thereby, to prevent the colorant layer 3from being abnormally transferred during the image formation procedure.Furthermore, by using a material having low dye dyeability as a primerlayer, it is possible to improve the printing density as compared withthat in case of the absence of a primer layer. The primer layer 4 is anoptional component of the thermal transfer sheet of the firstembodiment, and, for example, it may be formed with any of the followingorganic materials and inorganic materials. As the organic materials, forinstance, polyester based resins, polyacrylic acid ester based resins,polyvinyl acetate based resins, polyurethane based resins, styreneacrylate based resins, polyacrylamide based resins, polyamide basedresins, polyether based resins, polystyrene based resins, polyethylenebased resins, polypropylene based resins, vinyl based resins such aspolyvinyl chloride resins, polyvinyl alcohol resins, polyvinylpyrrolidone and modified forms thereof, and polyvinyl acetal basedresins such as polyvinyl acetoacetal and polyvinyl butyral, and thelike, may be exemplified. As the inorganic materials, for instance,colloidal inorganic pigment minute particles such as silica (colloidalsilica), alumina or alumina hydrate (alumina sol, colloidal alumina,cationic aluminum oxide or hydrates thereof, pseudo-boehmite, etc.),aluminum silicate, magnesium silicate, magnesium carbonate, magnesiumoxide, titanium oxide, and the like maybe exemplified. In addition,polymers having an inorganic main chain formed from: organic titanates,such as tetrakis (2-ethylhexyl) titanate, bis(ethyl-3-oxo-butanoaterate-0¹, 0³) bis(2-propanolate) titanium, or isopropyl triisostearoyltitanate; or titanium alkoxides, such as titanium tetra-isopropoxide ortitanium tetra-n-butoxide, may be used as the material for the primerlayer.

Further, by constituting the primer layer from the colloidal inorganicpigment minute particles, it is possible to prevent abnormal transfer ofthe colorant layer to the thermal transfer image-receiving sheet duringthe image formation more effectively. Further, during the imageformation, it is possible to prevent the colorant transition from thecolorant layer to the primer layer. This makes it possible to carry outthe diffusion of the colorant into the receiving layer side of thethermal transfer image-receiving sheet effectively, and thus it ispossible to form a high printing density image. As the colloidalinorganic pigment minute particles, colloidal silica, alumina sol areparticularly preferably used. With respect to the size of thesecolloidal inorganic pigment minute particles, it is preferable to usethem with an average primary particle diameter of not more than 100 nm,more desirably, not more than 50 nm.

By treating the surface of the substrate sheet 2, to which the colorantlayer 3 will be formed, with adhesive treatment, or by providing aprimer layer between the substrate sheet 2 and the colorant layer 3, itbecomes possible to improve the adhesion of the substrate sheet 2 andthe colorant layer 3, and to prevent the colorant layer 3 from beingabnormally transferred during the image formation. Furthermore, by usinga material having low dye dyeability as the primer layer, it is possibleto improve the printing density as compared with that in case of theabsence of a primer layer.

The primer layer can be formed by preparing a coating liquid for theprimer layer where one or more materials selected from the materialsenumerated as above are dispersed or dissolved in an appropriate solventsuch as an organic solvent, coating thus prepared coating liquid inaccordance with a known coating procedure such as the gravure printingmethod, the screen printing method, the reverse roll coating printingmethod using a gravure plate, or the like, and then drying the coatedsolution. Although there is no particular limitation about the coatingamount of the coating liquid for the primer layer, but usually it may beabout 0.02 g/m²-about 10 g/m² in terms of solid content.

(Colorant Layer)

As shown in FIG. 1, on one surface of the substrate sheet 2, thecolorant layer 3 is provided either directly, or indirectly via anoptional primer layer and the like. The colorant layer 3 is an essentialcomponent in the thermal transfer sheet of the first embodiment, and thecolorant layer 3 contains, a predetermined solvent, the colorantdispersible in the predetermined solvent, a dispersant, and a binderresin. Further, with respect to the thermal transfer sheet of the firstembodiment, it is characterized in that the dispersant which is includedin the colorant layer 3 is one or more kinds of dispersants selectedfrom the group consisting of polyether-based dispersants, graft typepolymer dispersants, acryl-based block type polymer dispersants,urethane-based polymer dispersants and azo-based dispersants.

According to the colorant layer 3 that satisfies the abovecharacteristics, in the thermal transfer sheet 1 of the firstembodiment, it is possible to prevent a kick and a scumming, whileexpanding the range of choices for colorants to be included in thecolorant layer 3. Further, the printed article to be formed can enjoyhigh durability, such as light resistance, and can prevent the printingdensity at the highlight portion from lowering, and further, can providea high quality photographic color image with gradation image by thesublimation transfer.

Hereinafter, advantages of the thermal transfer sheet 1 of the firstembodiment will be explained with exemplifying a thermal transfer sheet1X (See, FIG. 3) wherein a colorant layer 3C which includes a binderresin, a solvent, and a sublimable dye 10 y dissolvable in the solvent,is formed on the substrate. Here, FIG. 3 is a partial schematiccross-sectional view of a thermal transfer sheet schematically showingthe state of sublimable dye 10 y in the colorant layer 3C.

Since the sublimable dye 10 y dissolvable in the solvent may usuallyhave a low molecular weight and it is to be monomolecular, as shown inFIG. 3, the sublimable dye 10 y is present in a state of being localizedto the interfaces of the colorant layer 3C, wherein the colorant layer3C was formed by using a coating liquid where the sublimable dye hadbeen dissolved in a solvent. Thermal transfer sheet is generally storedat a rolled-up state, and in this rolled-up state, since the colorantlayer 3C and the back face layer are being directly in contact with eachother. Thus, under the state that the sublimable dye 10 y is present soas to be localized to the interfaces of the colorant layer 3C as shownin FIG. 3, when the thermal transfer sheet is stored at the rolled-upstate or the like, there is a tendency that the sublimable dye 10 y areeasily transferred to the back layer side of the substrate sheet 2. Thatis, in the case that a colorant layer 3C is simply provided on thesubstrate sheet 2 by using the coating liquid wherein the sublimable dye10 has been dissolved in a solvent, it is impossible to suppressoccurrences of the kick.

Meanwhile, when using a sublimable dye having a high molecular weight,and thereby, even possible to reduce the localization of the sublimabledye to the interfaces, it is difficult to prevent the occurrences ofkick and/or scumming unless the affinity of between the high molecularweight sublimable dye and the binder becomes sufficiently. In otherwords, with respect to the sublimable dye, to have a high molecularweight is preferable in view point of preventing the localization of thesublimable dye to the interfaces, whereas to have a high affinity withthe binder resin is preferable in view point of preventing theoccurrence of the kick and/or the scumming, but the sublimable dyeswhich can satisfy both of the above mentioned conditions areconsiderably restricted in their kinds, and thus, the range of choicesfor raw materials is forced to narrow.

Therefore, the thermal transfer sheet 1 of the first embodiment ischaracterized in that, as shown in FIG. 2, the colorant layer 3 providedon one surface of the substrate sheet 2 contains a binder resin, apredetermined solvent, a colorant 10 x, and a “specific dispersant”described later, and the colorant 10 x is the one that is dispersible inthe predetermined solvent. In other words, it is characterized in that,a colorant layer 3 is provided on one surface of the substrate sheet 2,the colorant layer being formed by using a coating liquid for thecolorant layer containing the “specific dispersant”, the binder resin,the colorant 10 x, and the predetermined solvent to which the colorant10 x is dispersible, and dispersing the colorant.

According to the colorant layer 3 containing the predetermined solventand the colorant 10 x dispersible to the predetermined solvent, as shownin FIG. 2, it is possible to allow the colorant 10 x to exist in a stateof being dispersed in the colorant layer 3. Thus, it becomes possible toprevent the occurrences of the kick and/or the scumming that may occurdue to the localization of the sublimable dye to the interfaces.Further, since the colorant layer 3 contains the “specific dispersant”described later, in addition to the colorant 10 x dispersible to thepredetermined solvent, it is possible to allow the colorant 10 xdispersible to the predetermined solvent to exist in a state of beingdispersed homogenously in the colorant layer, and thus, it becomespossible to prevent more effectively the occurrences of the kick and/orthe scumming, in cooperation with the effects of the above mentionedcolorant 10 x dispersible to the predetermined solvent. Here, FIG. 2 isa schematic partial sectional view of the thermal transfer sheetschematically showing the state of the colorant 10 x dispersible in apredetermined solvent which is contained in the colorant layer 3.Further, it should be noted that in FIG. 2, and FIG. 3 to 5, thesublimable dye 10 y and the colorant 10 x in the colorant layer areillustrated exaggeratingly.

“Binder Resin”

The colorant layer 3 contains a binder resin. The binder resin are theone that carries the colorant dispersible in the predetermined solvent.As the binder resins, for example, cellulose based resin such as methylcellulose, ethyl cellulose, hydroxyethyl cellulose, ethyl hydroxyethylcellulose, hydroxypropyl cellulose, cellulose acetate, cellulosebutyrate, nitrocellulose, etc.; vinyl based resin such as polyvinylalcohol, polyvinyl acetate, polyvinyl butyral, polyvinyl acetal,polyvinyl pyrrolidone, polyacrylamide, etc.; acryl based resins such aspoly (meth)acrylates, poly (meth)acryl amide, etc.; polyurethane basedresins; polyester based resins; phenoxy resins; and the like may beenumerated. Among them, cellulose based, vinyl based, acryl based,polyurethane based, and polyester based resins, etc., are preferred fromthe viewpoint of the heat resistance, the thermal transferability of thecolorant and the like. The binder resin may be used singly or in anymixture of two or more of them.

As the binder resin, further, releasing graft copolymers may also bementioned. The releasing graft copolymer may be also added as areleasing agent, in addition to the above mentioned binder resin.Herein, the above mentioned releasing graft copolymer donates the onewherein at least one releasing segment selected from the groupconsisting of polysiloxane segments, carbon fluoride segments,fluorinated hydrocarbon segments and long-chained alkyl segments isgraft-polymerized to a polymer main chain which constitutes any of theabove mentioned binder resins. As the releasing graft polymer, inparticular, the graft polymer which is obtained by graft-polymerizing apolysiloxane segment to a main chain consisting of polyvinyl acetal ispreferable. Furthermore, as a releasing agent for the purpose ofimproving releasing property, a silicone oil, a phosphoric acid ester, afatty acid ester or the like may be added.

“Predetermined Solvent”

The colorant layer 3 contains a solvent which is capable of dispersingthe colorant 10 x. The predetermined solvent contained in the colorantlayer 3 means a solvent capable of dispersing the colorant 10 x. Inother words, it means a solvent incapable of dissolving the colorant 10x. There is no particular limitation for the predetermined solvent, andcan be appropriately selected depending on the relationship with thecolorant 10 x contained in the colorant layer 3. As examples of thesolvent, for instance, organic solvent such as methyl ethyl ketone,toluene, xylene, methyl isobutyl ketone, ethyl acetate, isopropylalcohol, ethanol, etc., and water may be enumerated. As thepredetermined solvent, it is possible to use a kind of solvent singly,or to use in any mixture of two or more of them.

Here, it should be noted that, although the thermal transfer sheet ofthe first embodiment has an essential condition that the colorant layer3 contains a predetermined solvent, the condition does not intend todenote that the predetermined solvent capable of dispersing the colorant10 x is positively and actively contained in the colorant layer 3. But,the predetermined solvent contained in the colorant layer 3 refers to aresidual solvent contained in the colorant layer 3. With respect to theidentification of the residual solvent contained in the colorant layer3, it will be described later.

“Colorant Dispersible in the Predetermined Solvent”

The colorant layer 3 contains a colorant 10 x dispersible in thepredetermined solvent. The term “colorant” used herein is a conceptwhich also involves sublimable dyes, and pigments. There is noparticular limitation on the colorant 10 x dispersible in thepredetermined solvent, and can be appropriately selected depending onthe type of the predetermined solvent. Concretely, as long as thecolorant Ox is dispersible to the predetermined solvent which iscontained in the colorant layer 3, it may be any colorant.

As the colorant 10 x dispersible in the predetermined solvent, anycolorant can be appropriately selected from, for example, the sublimabledyes mentioned below and/or the pigments mentioned below, depending onthe solvent contained in the colorant layer 3. Concretely, apredetermined solvent is selected at first, and then, a colorant may beselected from, for example, the sublimable dyes mentioned below and/orthe pigments mentioned below, by a criterion whether it is dispersibleto the predetermined solvent or not.

As the sublimable dye, for instance, diarylmethane based dyes;triarylmethane based dyes; thiazole based dyes; merocyanine dyes;pyrazolone dyes; methine based dyes such as pyrazolone methine andpyridone methine; indoaniline based dyes; indonaphthole based dyes;azomethine dyes such as acetophenone azomethine dyes, pyrazoloazomethine dyes, imidazol eazomethine dyes, imidazo azomethine dyes, andpyridone azomethine dyes; xanthene based dyes; oxazine based dyes;cyanostyrene based dyes such as dicyanostyrene dyes and tricyanostyrenedyes; thiazine based dyes; azine based dyes; acridine based dyes;benzeneazo based dyes; azo based dyes such as, pyridoneazo dyes,thiopheneazo dyes, isothiazoleazo dyes, pyrroleazo dyes, pyrazoleazodyes, imidazoleazo dyes, thiadiazoleazo dyes, triazoleazo dyes, anddisazo dyes; spiropyran based dyes; indolinospiropyran based dyes;fluoran based dyes; rhodaminelactam based dyes; naphthoquinone baseddyes; anthraquinone based dyes; quinophthalone based dyes; aminopyrazolebased dyes; pyrazolotriazole based dye; styryl based dyes such asdicyano styryl and tricyano styryl; etc., can be enumerated.

Concretely, for instance, C. I. (Color index) Disperse Yellow 51, 3, 54,79, 60, 23, 7, 141, 201, 231; C. I. Disperse Blue 24, 56, 14, 301, 334,165, 19, 72, 87, 287, 154, 26, 354; C. I. Disperse Red 135, 146, 59, 1,73, 60, 167; C. I. Disperse Orange 149; C. I. Disperse Violet 4, 13, 26,36, 56, 31; C. I. Solvent Yellow 56, 14, 16, 29, 93; C. I. Solvent Blue70, 35, 63, 36, 50, 49, 111, 105, 97, 11; C. I. Solvent Red 135, 81, 18,25, 19, 23, 24, 143, 146, 182; C. I. Solvent Violet 13; C. I. SolventBlack 3; C. I. Solvent Green 3; and the like may be enumerated. As thesublimable dye, from the viewpoint of having a light resistance and alsoa high intensity, the quinophthalone based dyes, anthraquinone baseddyes are preferable, and further, the quinophthalone based dyes areparticularly preferable.

As the quinophthalone based dyes (colorant), quinophthalone basedcolorants represented by the following formula 1 are preferred. Bycontaining a quinophthalone based dye represented by the formula 1 inthe colorant layer 3, it becomes possible to improve the lightresistance and the sharpness of a printed article that is formed usingthe thermal transfer sheet of the first embodiment. With respect to thequinophthalone based colorant represented by Formula 1, when both X andR¹ are a hydrogen atom, individually, it represents a Disperse Yellow54. Also, when X is Br, and R¹ is hydrogen atom, it represents DisperseYellow 64. As quinophthalone-based colorants represented by thefollowing formula 1, Disperse Yellow 149, and further, thequinophthalone dyes described in JP Hei 10-287818 A and the like can beenumerated. The related content of this reference are incorporatedherein by reference.

Wherein, X represents a hydrogen atom or a halogen atom, R¹ represents ahydrogen atom, an alkyl group or derivative thereof having 1 to 5 carbonatoms, an acyl group including an alkyl group or a benzoic ring andhaving a total carbon number of 6 to 10.

As the sublimable dye, it is also possible to use any commerciallyavailable product as-is. For instance, as a yellow dye, Holon brilliantyellow-S-6GL (manufactured by Sandoz, Disperse Yellow 231), MACROLEXYellow 6G (manufactured by Bayer, Disperse Yellow 201); as a magentadye, MS-Red-G (manufactured by Mitsui Toatsu Chemicals, Inc., DisperseRed 60), Macrolex Red Violet R (manufactured by Bayer, Disperse Violet26); as a cyan dye, Kayaset Blue 714 (manufactured by Nippon Kayaku Co.,Ltd., Solvent Blue 63), Holon Brilliant Blue S-R (manufactured bySandoz, Disperse Blue 354), Waxoline Blue AP-FW (manufactured by ICI,Solvent Blue 36); etc., are exemplified.

As the sublimable dye dispersible in the predetermined solvent, it ispossible to use one kind of the sublimable dye singly, or to use in anymixture of two or more of them. As a dispersible colorant in apredetermined solvent, the sublimable dye(s) may also be used incombination with pigment(s). It can also be used in combination of twoor more pigments. Here, the colorant layer 3 has to contain at least oneof the color material(s) 10 x dispersible in any solvent(s) which iscontained in the colorant layer 3, provided that none of the solventsincluded in the colorant layer 3 can dissolve the dispersible colorant10 x. This is because, even in the case that the colorant layer 3contains a predetermined solvent and a colorant 10 x dispersible to thepredetermined solvent, if the colorant 10 x can be dissolved by anyother solvent included in the colorant layer 3, the dispersible colorant10 x would exist in its dissolved condition in the coating liquid forthe colorant layer as a consequence.

When pigment(s) is used as the colorant 10 x dispersible in apredetermined solvent, the pigment(s) may be suitably selected fromknown organic or inorganic pigments. As the pigment, the one which has asufficient color density, and is not easily discolored or faded bylight, heat or the like, is preferable. As the color of the pigments, itis possible to use various colors of the coloring agents, without beinglimited to cyan, magenta, yellow and black.

As examples of the pigment, azo based pigments, phthalocyanine basedpigments, quinacridone based pigments, perylene-perinone based pigments,isoindolinone based pigments, isoindoline based pigments, dioxazinebased pigments, quinophthalone based pigments, diketopyrrolopyrrolebased pigments, anthraquinone based pigments, thioindigo based pigments,metal complex based pigments and the like may be enumerated. Among theseorganic pigments, C. I. Pigment Yellow 138, C. I. Pigment Yellow 150, C.I. Pigment Green 7, C. I. Pigment Green 36, C. I. Pigment Red 122 and C.I. Pigment Violet 19 are desirable from the viewpoint of having highluminance.

Although the quinophthalone-based colorant represented by the aboveformula 1 which mainly has a hue of yellow, it is preferable to use acolorant (pigment) represented by the following formula 2 to thecolorant layer, in addition to the above mentioned quinophthalone-basedcolorants represented by the above formula 1, from the viewpoint ofimproving the dispersibility of the colorants and the stability of theink, and the viewpoint of preventing the contamination due to thetransfer of the colorants from the colorant layer and the retransfer ofthis transferred colorants.

wherein, each of R¹-R⁵ represents independently a hydrogen atom, an arylgroup or derivative thereof having 1 to carbon atoms, or a sulfonatedderivative having at least one sulfonic acid group (—SO₃H) orsulfonamide group.

Among the colorants (pigments) represented by the above formula 2, theones wherein at least one of R¹-R⁵ is the sulfonated derivative havingat least one sulfonic acid group (—SO₃H) or sulfonamide group arepreferable. Furthermore, a part of or all of the sulfonic acid group(s)may take a salt form by salifying with amine, ammonium hydroxide,chloride, bromide, etc., or a metal. A derivative of the colorantrepresented by Formula 2 is represented by the following formula 3.

It is preferable to use the sulfonated derivative represented as aboveformula as the colorant, because it can brings many advantages such as,to enhance the adhesiveness with the substrate sheet of the thermaltransfer sheet, to enhance the dispersibility of the colorants in thecolorant layer, etc. Here, with respect to the sulfonated derivative,albeit at a hue of yellow, since its hue is slightly changed as comparedwith the hue of quinophthalone-based colorants represented by the aboveformula 1, it is preferable to use in a small proportion, that is, toadd at not more than 15% (by weight) of the total of colorants, from theviewpoint of the color reproduction.

Further, the thermal transfer sheet 1 of the first embodiment ischaracterized in that the colorant layer 3 contains a dispersant, andthe dispersant is one or more kinds of dispersants selected from thegroup consisting of polyether-based dispersants, graft type polymerdispersants, acryl-based block type polymer dispersants, urethane-basedpolymer dispersants and azo-based dispersants. Hereinafter, thesedispersants may be referred to collectively as “specific dispersants”,occasionally.

As the polyether-based dispersants, for example, polyether basedcarboxylic acids, polyether based phosphoric acids, polyether basedphenols, and the like can be enumerated. As commercially availableproducts of the polyether-based dispersants, for instance, DISPARLONDA234, DISPARLON DA325, (trade names of Kusumoto Chemicals, Co., Ltd.),Solsperse 20000 (The Lubrizol Corporation), etc., may be enumerated.

The graft-type polymer dispersant denotes a polymer having a structurewherein branch polymer segment(s) is grafted to a main polymer segmentwhich has a plural number of functional groups such as basic groups, forinstance, a polymer of which the main polymer segment is polyallylamineand the branch polymer segment is ε-caprolactone ring-openingpolymerized polymer may be enumerated. As the dispersant of the abovegraft-type polymer, for instance, Ajisper PB821, Ajisper PB822, AjisperPB823, Ajisper PB824, Ajisper PB827, Ajisper PB880, and mention may bemade of Ajisper PB881 (manufactured by Ajinomoto Fine-Techno Co., Ltd.),etc., may be enumerated. As the graft-type polymer dispersant, it ispossible to use one kind of the dispersants singly, or to use in anycombination of two or more of them.

As the acryl based block type polymer dispersant, those which has, asthe main chain structure, for example, methacryl based resin or acrylbased resin or the like, may be enumerated. Especially, dispersants ofmethacrylic or acrylic block type polymer including tertiary aminogroups are preferred. The weight average molecular weight (Mw) of theblock type polymer dispersant is preferably in the range of not lessthan 500 or not more than 20 000, more preferably, in the range of notless than 1,000 and not more than 15,000, still more preferably, in therange of not less than 3000 and not more than 12000. When using theacryl based block type polymer dispersant having a weight averagemolecular weight within the above preferred range, it is possible toachieve both the wettability and dispersion stability to the colorant atthe initial stage of dispersion to disperse uniformly the colorant.Incidentally, the weight average molecular weight (Mw) used hereindenotes a value measured by the gel permeation chromatography (GPC) andcalibrated with polystyrene standard. As the dispersant of themethacrylic or acrylic block type polymer including tertiary aminogroups, for instance, Disperbyk-2000, Disperbyk-2001, BYK-LPN6919,BYK-LPN21116, BYK-LPN21324 (manufactured by BYK Additives & Instruments)may be enumerated. As the acryl based block type polymer dispersant, itis possible to use one kind of the dispersants singly, or to use in anycombination of two or more of them.

As the urethane based polymer dispersant, an urethane based block-typepolymer dispersant is preferable used. The weight average molecularweight (Mw) of this block type polymer dispersant is preferably in therange of not less than 4000 and not more than 300,000, more preferablynot less than 5,000 and not more than 200,000, further preferably, inthe range of not less than 6,000 and more than 100,000, and furthermorepreferably, in the range of not less than 10,000 and not more than50,000. As the above mentioned block type polymer dispersant, forexample, “BYK-161, BYK-162, BYK-163, BYK-164, BYK-167”, manufactured byBYK Additives & Instruments; “EFKA 4047, 4050, 4010, 4165”, manufacturedby BASF; etc. may be enumerated. As the urethane based polymerdispersant, it is possible to use one kind of the dispersants singly, orto use in any combination of two or more of them.

As the azo-based dispersant, azo pigment derivatives may preferably beused. As the azo pigment derivative, for instance, Solsperse 22000(manufactured by The Lubrizol Corporation) may be enumerated. As the azobased dispersant, it is possible to use one kind of the dispersantssingly, or to use in any combination of two or more of them.

Although there are many dispersants for dispersing the colorant 10 xdispersible to the predetermined solvent is present a number, but in thepresent invention, since the colorant layer 3 contains the “specificdispersant”, it is possible to keep the dispersion stability of thecolorant 10 x dispersible to the predetermined solvent at a high level.Incidentally, when the colorant layer contains a dispersant other thanthe “specific dispersant”, its preventing ability for kick and scumming,light resistance, printing quality of a printed article to be formed islowered, as compared to those obtained by the colorant layer 3containing the “specific dispersant”. As the “specific dispersant”, itis possible to use one kind of the dispersants singly, or to use in anycombination of two or more of them. The content of the “specificdispersant” is usually in the range of not more than 100 parts byweight, preferably in the range of 0.5 to 100 parts by weight, morepreferably, 1 to 70 parts by weight, and particularly preferably, 10 to50 parts by weight, on the basis of 100 parts by weight of thecolorants. When the content of “a specific dispersant” is more than 100parts by weight, there is a possibility that the sharpness may beimpaired. On the other hand, when the content of the “specificdispersants” is too small, there is a possibility that the functions asthe “specific dispersants” cannot be sufficiently exhibited. Next,preferred combinations of the colorant and the “specific dispersant” isthe colorant layer containing 3 will be described by taking someexamples. Incidentally, the colorants and the “specific dispersants”contained in the colorant layer 3 are not limited to the followingcombinations. As long as the condition that the colorant layer 3contains a predetermined solvent, a colorant dispersible to thepredetermined solvent, a “specific dispersant”, and a binder resin issatisfied, it is possible to suppress the occurrence of the kick and/orthe scumming, and the lowering of print density in the highlight portionin the thermal transfer sheet provided with the colorant layer, and alsopossible to improve durability such as light resistance of the printedarticle to be formed by the thermal transfer sheet, and to obtain a highquality image.

The colorant layer 3 of a preferred example contains thequinophthalone-based colorant represented by the above formula 1, thecolorant represented by the above formula 2, the acryl based block typepolymer dispersant, the predetermined solvent, and a binder resin. Inother words, the colorant layer 3 of this preferred example is acolorant layer which is formed by using a coating liquid for colorantlayer which includes the quinophthalone-based colorant represented bythe above formula 1, the colorant represented by the above formula 2,the acryl based block type polymer dispersant, the predeterminedsolvent, and a binder resin. According to the coating liquid forcolorant layer which includes the quinophthalone-based colorantrepresented by the above formula 1, the colorant represented by theabove formula 2, the acryl based block type polymer dispersant, thepredetermined solvent and the binder resin, it is possible to dispersethe quinophthalone-based colorant represented by the above formula 1with a small particle diameter, concretely, with a particle diameter ofnot more than 200 nm, in the coating liquid for colorant layer.Therefore, by constituting a thermal transfer sheet comprising acolorant layer formed by using the coating liquid for colorant layer asabove mentioned, in addition to the above effects, it becomes possibleto form an image of high concentration, and also possible to improve theadhesion between the substrate sheet 2 and the colorant layer 3.

The colorant layer 3 of another preferred example contains thequinophthalone-based colorant represented by the above formula 1, apredetermined solvent, the urethane based polymer dispersant, the azobased dispersant, and a binder resin. In other words, the colorant layer3 of this preferred example is a colorant layer which is formed by usinga coating liquid for colorant layer which includes thequinophthalone-based colorant represented by the above formula 1, apredetermined solvent, the urethane based polymer dispersant, the azobased dispersant, and a binder resin. In such the coating liquid forcolorant layer which includes the colorant and the dispersants in theabove mentioned combination, it is also possible to disperse thequinophthalone-based colorant represented by the above formula 1 with aparticle diameter of not more than 200 nm, in the coating liquid forcolorant layer, same as the colorant layer of the above mentioned firstexample.

With respect to the blending ratio of the urethane based dispersant andthe azo-based dispersant, although there is no particular limitation, itis preferable to be in the range of about 9:1 to about 1:9, in theirweight ratio.

The colorant layer 3 of further another preferred example is a colorantlayer which is formed by using a coating liquid for colorant layer whichis prepared by a “specific preparation method of the coating liquid forcolorant layer”. The “specific preparation method of the coating liquidfor colorant layer” is a method where a dispersion containing thecolorant in the predetermined solvent is prepared by using the “specificdispersant” under a condition of containing no or a very small amount ofthe binder resin, and thereafter, a binder resin is added to theobtained dispersion as post-addition in order to obtain the coatingliquid for colorant layer”. According to the coating liquid for colorantlayer prepared by this preparation method, it is possible to dispersethe colorant with a small particle diameter in a short time, as comparedwith the coating liquid for colorant layer which is prepared bydispersing the colorant in the predetermined solvent with using the“specific dispersant” under the presence of the binder resin.

“Determination Method for Dispersibility of Colorant to PredeterminedSolvent”

By the following method, it is possible to determine whether a colorantof interest to be contained in the colorant layer can be dispersed inthe predetermined solvent or not. To the predetermined solvent, thecolorant of interest is added so as to be an amount of 2 w/v %, then thecolorant added solvent is heated for 1 hour at 50° C. with stirring.Then, the resulting liquid is left standing for 60 hours at 25° C., andafter the leaving, the liquid is observed visually about the presence orabsence of precipitation of the colorant of interest. When precipitationof the colorant of interest does not observed visually, the colorant ofinterest can be determined to be a colorant soluble in a predeterminedsolvent. On the other hand, when precipitation of the colorant ofinterest is observed visually, the colorant of interest can bedetermined to be a colorant insoluble to the predetermined solvent, inother words, a colorant dispersible to the predetermined solvent. Withrespect to the sublimable dye, it is possible to determine thedispersibility in the same manner. With respect to the colorant layer ofthe thermal transfer sheet of the second embodiment described later, andthe colorant layer of the thermal transfer sheet of the thirdembodiment, it is also possible to determine the dispersibility in thesame manner.

“Determination Method for Colorant, Residual Solvent”

For instance, by the following method, it is possible to determinewhether a thermal transfer sheet of interest (hereinafter, referred toas target thermal transfer sheet) satisfies the matters specifying thethermal transfer sheet of the first embodiment or not. First, thecolorant layer of the target thermal transfer sheet is analyzed in orderto identify the colorant component contained in the colorant layer. Asthe identification method of the colorant components, any conventionallyknown analytical method such as the nuclear magnetic resonancespectroscopy, IR spectroscopy or the like is applicable.

Then, the kind of the solvent remaining in the colorant layer isdetermined. As the identification method of the kind of the solvent, forexample, the gas chromatography is applicable. In the identification ofthe kind of the solvent by the gas chromatography, for instance, a gaschromatography analyzer such as Gas Chromatography GC14-A, manufacturedby Shimadzu Corporation, and the like can be utilized. Incidentally, inorder to eliminate the influence of the solvents which have beencontained in the substrate sheet, back face layer, and/or any arbitrarylayers in the target thermal transfer sheet, it is necessary to analyzeto the layer corresponding to the colorant layer of the target thermaltransfer sheet on the identification of the kind of the solvent.Concretely, when the kind of the solvent remaining in the colorant layeris determined by using the gas chromatography method, it is important totake only a part of the layer corresponding to the colorant layer of thetarget thermal transfer sheet and carry out the analyze to the portion.

When at least one of the identified colorant components as mentionedabove is the colorant component dispersible in the identified solvent asmentioned above, and the above “specific dispersant” is contained as thedispersant, the target thermal transfer sheet can be judged as beingsatisfying the matters specifying the thermal transfer sheet of thefirst embodiment. Using the “determination method for dispersibility ofcolorant to predetermined solvent”, it is possible to identify whetherthe identified colorant component is soluble or dispersible in theidentified solvent.

The colorant layer 3 may contain other optional additives, for instance,a releasing agent for improving releasability from the receiving layerof the thermal transfer-image receiving sheet, an antistatic agent, anorganic or inorganic filler for controlling the lubricity with thereceiving layer, etc., in addition to the essential components, i.e.,the binder resin, the predetermined solvent, the colorant dispersible tothe predetermined solvent, and one or more kinds of dispersants selectedfrom the group consisting of polyether-based dispersants, graft typepolymer dispersants, acryl-based block type polymer dispersants,urethane-based polymer dispersants and azo-based dispersants.

As the release agent, for instance, silicone oils, polyethylene waxes,amide waxes, Teflon (registered trademark), surfactants such as fluorinebased surfactants or phosphoric ester based surfactants may beexemplified. Although there is no particular limitation on the contentof the release agent in the colorant layer, it is preferable to be inthe range of not less than 0.1% by weight and not more than 10% byweight on the basis of the total solid content of the binder resincontained in the colorant layer. By incorporating the release agent inthis range, even when the receiving layer does not contain a releaseagent, it is possible to sufficiently satisfy the releasing propertybetween the colorant layer 3 and the receiving layer.

There is no particular limitation on the method of forming the colorantlayer 3, and for instance, the colorant layer 3 can be formed bypreparing a coating liquid for the colorant layer where the binderresin, the predetermined solvent, the colorant dispersible to thesolvent, and the “specific dispersant”, and any optionally addedcomponent(s) are used and the colorant is dispersed in the predeterminedsolvent, coating thus prepared coating liquid for colorant layer inaccordance with a known coating procedure such as the gravure printingmethod, the screen printing method, the reverse roll coating printingmethod using a gravure plate, or the like, and then drying the coatedsolution. The coating amount of the coating liquid for colorant layer isnot particularly limited, but usually, it is in the range of about 0.2g/m²-about 10 g/m² in term of the solid content.

(Back Face Layer)

As shown in FIG. 1, in the thermal transfer sheet of the firstembodiment, a back face layer 5 may be provided on a backside surface ofthe substrate 1, that is, the surface which is different from anothersurface on which the colorant layer is provided, in order to preventadverse effects such as sticking or wrinkles due to heat from thethermal head, to impart slipperiness to the thermal transfer printer orthe like, and enhance transportability of the sheet therein. As theresin for forming the back face layer, any conventionally known resinmay be used, for instance, thermoplastic resins such as polyester typeresins, polyacrylic ester type resins, polyvinyl acetate type resins,styrene acrylate type resins, polyurethane type resins, polyolefin typeresins such as polyethylene type resins and polypropylene type resins,polystyrene type resins, polyvinyl chloride type resins, polyether typeresins, polyamide type resins, polyimide type resins, polyamide-imidetype resins, polycarbonate type resins, polyacrylamide type resins,polyvinyl chloride resins, polyvinyl butyral resins, and polyvinylacetal resins; and silicone-modified forms of these thermoplastic resinsmay be enumerated. Concretely, for example, polyvinyl butyral resins,polyvinyl acetoacetal resins, polyester resins, vinyl chloride-vinylacetate copolymers, polyether resins, polybutadiene resins,styrene-butadiene copolymers, acryl polyols, polyurethane acrylates,polyester acrylates, polyether acrylates, epoxy acrylates, urethane orepoxy prepolymers, nitrocellulose resins, cellulose nitrate resins,cellulose acetopropionate resins, cellulose acetate butyrate resins,cellulose acetate hydrodiene phthalate resins, cellulose acetate resins,aromatic polyamide resins, polyimide resins, polyamide-imide resins,polycarbonate resins, and chlorinated polyolefin resins and the like maybe enumerated.

As a slipping property-imparting agent to be added to the back facelayer comprising above mentioned resin or to be overcoated on the backface layer, for instance, phosphoric acid esters, fatty acid esters,metallic soaps, waxes, silicone oils, graphite powders, silicone basedgraft polymers, fluorine containing graft polymers, acrylic siliconegraft polymers, silicone polymers such as acrylic siloxanes and arylsiloxanes may be exemplified. However, it is preferable to be a layerwhich comprises a polyol such as a polyalcohol polymer compound, and apolyisocyanate compound and a phosphoric acid ester-based compound, andfurther, it is more preferably to further add a filler. Further,phosphate esters, fatty esters, metallic soaps, waxes, etc. may be alsopreferably used.

As the metal soaps, for instance, multivalent metallic salts of alkylphosphoric esters, multivalent metal salts of fatty acids, metallicsalts of alkyl carboxylic acid may be enumerated. As the metal soaps,the ones which are known in the art as additive for plastics may beused. Among them, zinc stearate and/or zinc stearyl are preferred.

As the phosphoric acid ester, for example, (1) phosphoric diesters ormonoesters of saturated or unsaturated higher alcohols having a carbonnumber of 6 to 20, (2) phosphoric monoesters or diesters ofpolyoxyalkylene alkyl ethers or polyoxyalkylene alkyl allyl ethers, (3)phosphoric diesters or monoesters of alkylene oxide adducts (averageaddition molar number: 1-8) of the above mentioned saturated orunsaturated alcohols, (4) phosphoric monoesters or diesters of alkylphenols or alkyl naphthols which have an alkyl group having a carbonnumber of 8-12, are enumerated. As the saturated and unsaturated higheralcohols for the above (1) and (3) compounds, for example, cetylalcohol, stearyl alcohol, oleyl alcohol, etc., are enumerated. As thealkyl phenol for the above (3) compounds, for example, nonyl phenol,dodecyl phenol, diphenyl phenol, etc., are enumerated.

There is no particular limitation about the method for forming the backface layer. The back face layer 3 may be formed by dissolving ordispersing the above exemplified resin, and optionally, otheringredients such as lubricant into a suitable solvent; coating thusprepared coating liquid onto the substrate 2 in accordance with a knowncoating procedure such as the gravure printing method, the screenprinting method, the reverse roll coating method using a gravure plate,or the like; and then drying the coated liquid. As the solvent to beused for preparing the coating liquid, for instance, water, toluene,methyl ethyl ketone, ethanol, isopropyl alcohol, cyclohexane, dimethylformamide, ethyl acetate, etc., can be enumerated. The coating amount ofthe coating liquid for back face layer is not limited as long as theanti-fusion property, the lubricity or the like is fulfilled, andusually, it is in the range of about 0.1 g/m²-about 3 g/m² in term ofthe solid content.

(Back Face Primer Layer)

Further, in the thermal transfer sheet of the first embodiment, a backface primer layer (not shown) can also be provided between the substratesheet 2 and the back face layer 5. The back face primer layer is a layerprovided for improving the adhesion between the substrate sheet 2 andthe back surface layer 5, and it is an optional layer. As the back faceprimer layer, for example, polyester resins, polyurethane resins,acrylic resins, polycarbonate resins, polyamide resins, polyimideresins, polyamideimide resins, vinyl chloride-vinyl acetate copolymers,polyvinyl butyral resins, polyvinyl alcohol resins, polyvinylpyrrolidone resins and the like may be enumerated. It may also contain aconductive material for imparting appropriate conductivity. For example,sulfonated polyaniline, carbon particles, silver particles, goldparticles, and the like may be enumerated.

As described above, the thermal transfer sheet according to the firstembodiment of the present invention is fairly explained. However,without deviating from the scope and the spirit of the first embodimentof the present invention, the thermal transfer sheet can takes variousmodified embodiments other than the ones as disclosed above. Forexample, in the constitution shown in FIG. 1, it is possible to providethe above-mentioned colorant layer 3 and a transferable protective layer(not shown) are provided on the same surface of the substrate sheet 2 asbeing frame sequentially in order to manufacture an integral typethermal transfer sheet. In addition, it is also possible to providecolorant layers having each individual hue different from each other onthe same surface of the substrate sheet 2 as being frame sequentially.For instance, it is possible to provide a yellow colorant layer, amagenta colorant layer, and a cyan colorant layer on the substrate sheet2 so as to the dye layers are layered in parallel on the substrate sheet2 across the surface of the substrate sheet, as being framesequentially. In this case, as long as at least one colorant layer ofthese colorant layers provided as being frame sequentially is thecolorant layer 3 as above described, it can be embraced in the firstembodiment of the present invention.

<<Coating Liquid for Colorant Layer of the First Embodiment>>

Next, the coating liquid for colorant layer of the first embodiment ofthe present invention will be described below. The coating liquid forcolorant layer of the first embodiment is the coating liquid for formingthe above explained colorant layer of the thermal transfer sheet of thefirst embodiment, and is characterized in that it contains apredetermined solvent, a colorant dispersible to the predeterminedsolvent, a dispersant, and a binder resin.

The coating liquid for colorant layer of the first embodiment is furthercharacterized in that the colorant dispersible in the predeterminedsolvent is dispersed in a particle size of not less than 50 nm and notmore than 300 nm in the coating liquid for colorant layer; and, thedispersant is the above mentioned “specific dispersant(s)”, i.e., one ormore kinds of dispersants selected from the group consisting ofpolyether-based dispersants, graft type polymer dispersants, acryl-basedblock type polymer dispersants, urethane-based polymer dispersants andazo-based dispersants. With respect to the coating liquid for colorantlayer of the first embodiment, although the particle size of thecolorant dispersible to the predetermined solvent is defined as above,the particle size of the colorant used herein denotes the averagedispersed particle diameter of the colorant in the coating liquid forcolorant layer in the first embodiment. Concretely, it is a dispersedparticle diameter of the colorant particles dispersed in a dispersionmedium of the coating liquid, and it is determined by a laser lightscattering particle size distribution meter. With respect to themeasurement of the particle diameter by the laser light scatteringparticle size distribution meter, the coating liquid to be measured isappropriately diluted to a concentration that is capable of beingmeasured by the laser light scattering particle size distribution meter(for example, 1000-fold dilution, etc.) with the same predeterminedsolvent as being contained in the coating liquid, and then the particlediameter can be determined by using the laser light scattering particlesize distribution analyzer (for example, Nanotrac particle sizedistribution analyzer UPA-EX150, manufactured by Nikkiso Co. Ltd.) inaccordance with the dynamic light scattering method at 23° C. Theaverage dispersed particle diameter used herein is a volume averageparticle size.

Further, with respect to the coating liquid for colorant layer of thefirst embodiment, the “colorant in the coating liquid for colorant layerare dispersed” denotes the condition that no precipitation of thecolorant particles is observed visually after 120 hours (5 days)standing of the coating liquid for colorant layer at 20-25° C. Withrespect to the coating liquid for colorant layer of the firstembodiment, it is defined that the colorant dispersible to thepredetermined solvent is dispersed in a particle diameter of not lessthan 50 nm and not more than 300 nm in the coating liquid for colorantlayer. This is because, if the particle diameter of the colorantdispersed is less than 50 nm, there is a tendency that the colorantcaused gelation due to an interaction with the binder resin, and thecoating liquid owns the same properties as the state of the colorant isdissolved, and as a result, background stain (stains at the non-printingportion is caused) is likely to occur during printing. On the otherhand, if the particle diameter of the colorant dispersed is more than300 nm, there is a tendency that the precipitation of the colorant iseasily caused by variation of the coating liquid for colorant layer withtime, and, also the transfer sensitivity becomes insufficient, and thedesired print density cannot be obtained.

In the coating liquid for colorant layer of the first embodiment, it ispreferable that the colorant dispersible in the predetermined solvent isin the range of 50-300 parts by weight, and more desirably, in the rangeof 85-250 parts by weight, on the basis of 100 parts by weight of thebinder resin. Furthermore, it is preferable that the colorantdispersible in the predetermined solvent is in the range of 0.5-20% byweight on the basis of the total weight of the coating liquid forcolorant layer of the first embodiment. Furthermore, the total weight ofthe colorant dispersible in the predetermined solvent, the binder resinand the “specific dispersant(s)” to the total weight of the coatingliquid for colorant layer of the first embodiment, that is, the solidcontent is preferably in the range of 2-40% by weight, and morepreferably in the range of 5-35% by weight. Incidentally, when thecoating liquid for the colorant layer of the first embodiment containstwo or more kinds of colorants dispersible in the predetermined solvent,both the content and the solid content of the above colorant representthe total amount of the individual color materials.

It is preferable that as the colorant dispersible in the predeterminedsolvent, a dye such as Disperse Yellow 54, and a pigment represented bythe Formula 3 are mixed and contained in the coating liquid for colorantlayer of the first embodiment, form the view point that the ink becomesgood, and the printed articles becomes excellent in durability such aslight resistance, and it becomes possible to enhance the transfersensitivity during printing. The colorant layer of the thermal transfersheet is a layer containing a colorant for thermal transition by heatingwith a thermal head or the like, by sublimation or the like, and thus,it is preferable to mix the pigment to the above mentioned dye as themain ingredient. In detail, when using the pigment, it is preferable tomix the dye and the pigment in a range of dye/pigment=7/3 to 9.5/0.5(weight ratio).

The details for the predetermined solvent the colorant dispersible inthe predetermined solvent, the “specific dispersant(s)”, and the binderresin, which are essential components of the coating liquid for colorantlayer of the first embodiment, are the same with those described abovein the explanation about the colorant layer of the thermal transfersheet. Further, as a preferred combination of the “specificdispersant(s)” and the colorant dispersible to the predetermined solventin the coating liquid for colorant layer of the first embodiment, thecombinations described above in the explanation about the colorant layer3 of the thermal transfer sheet of the first embodiment can be cited. Inthe coating liquid for colorant layer of the first embodiment, it ispossible to add optionally any of various additives known in the art, ifnecessary, in addition to the essential components. As the optionaladditives, for instance, polyethylene wax, silane coupling agent,organic minute particles, inorganic minute particles and the like may beenumerated.

“First Method for Preparation of Coating Liquid for Colorant Layer”

The coating liquid for colorant layer of the first embodiment can beprepared in accordance with a known preparation method in the art using,for example, a paint shaker, a propeller type stirrer, a dissolver, ahomomixer, a ball mill, a bead mill, a sand mill, a biaxial roll mill, atriaxial roll mill, an ultrasonic dispersing machine, a kneader, a linemixer, a biaxial extruder or the like. As one approach to preparing thecoating liquid for colorant layer of the first embodiment, in the caseof using a bead mill, or a ball mill, as for the beads, the balls to beused, glass, ceramic, steel, zirconia and the like may be enumerated.Among them, zirconia beads are especially desirable from the viewpointof hardness, wear resistance, specific gravity and particle size. As thediameter of the beads, it is preferable to be in the range of 0.05-2.0mm, and particularly, it is preferable to select the bead diameterdepending on the initial particle diameter of the colorant.

“Second Method for Preparation of Coating Liquid for Colorant Layer ofFirst Embodiment”

Further, as another method for preparing the coating liquid for colorantlayer of the first embodiment, there is a method where, at a high shearrate, the colorant dispersible to the predetermined solvent, the“specific dispersant(s)”, and a lump of the binder resin are kneaded,then the predetermined solvent is added, and the colorant dispersible tothe predetermined solvent is dispersed in the added predeterminedsolvent with using a paint shaker. For instance, an ink which underwentdispersing treatment by using Ultra Visco Mill UVM-2, manufactured byAIMEX Co., Ltd., with zirconia beads (average diameter of 0.3 mm) at arotation rate of 1000 rpm for 10 hours, and a colorant dispersible tothe predetermined solvent, “specific dispersant(s)”, a binder resin anda solvent are kneaded by using a biaxial roll mil, manufactured byKansai Roll Co., Ltd., under the conditions of roll temperature of 20°C., roll rotation rate for front roll of 20 rpm, and roll rotation ratefor rear roll of 24 rpm, and then the solvent is further added tokneaded product, and they underwent dispersion using a paint shaker, inorder to prepare the coating liquid for colorant layer of the firstembodiment. With respect to both of the coating liquids for colorantlayer of the first embodiment which were prepared in accordance witheither one of the above two methods, it has been confirmed that theparticle size distribution of the colorant in the coating liquid is inthe range of 50 nm-300 nm in the diameter on the measurement inaccordance with the above mentioned measurement method of the particlesize distribution.

“Method for Preparation of Coating Liquid for Specific Colorant Layer(Third Method for Preparation of the Coating Liquid for Colorant Layerof the First Embodiment)”

In the above two methods, in the presence of the binder resin, by usingthe “specific dispersant(s)”, the colorant dispersible in thepredetermined solvent is dispersed in the predetermined solvent.However, depending on the type of the binder resin contained in thecoating liquid for colorant layer of the first embodiment, the binderresin may interfere in the dispersibility of the colorant owing to the“specific dispersant(s)”. Thus, in the “method for preparation ofcoating liquid for specific colorant layer”, in order to sufficientlyexhibit the dispersibility of the colorant owing to the “specificdispersant(s)”, under the condition that no binder resin or a littleamount of binder resin exists, a dispersion where the colorant isdispersed in the predetermined solvent is prepared by using the“specific dispersant(s)”. Then, the binder resin, or a liquid containingthe binder resin is post-added to the above mentioned dispersion, inorder to prepare the coating liquid for colorant layer which containsthe predetermined solvent, the colorant dispersible in the predeterminedsolvent, the “specific dispersant(s)”, and a binder resin. According tothis preparation method, it is possible to disperse the colorant intothe predetermined solvent, under the condition of being free from, orreceiving little extent of, the influence of the binder resin whichbecomes a factor of interfering in the dispersibility of the colorantowing to the “specific dispersant”. Thus, as compared with the abovementioned two methods, it is possible to allow the colorant to existwith a smaller particle size in the finally prepared coating liquid forcolorant layer of the first embodiment. This preparation method can becarried out by appropriately selecting and using procedures in the abovementioned two methods, except the points that the colorant undergoesdispersing under the condition that the binder resin does not exist, orexists in a small amount, and that the binder resin is post-added afterthe colorant has been dispersed.

The coating liquid for colorant layer of the first embodiment, inaddition to the above essential components, may contain any optionalingredient(s).

<<Method of Manufacturing Thermal Transfer Sheet of the FirstEmbodiment>>

Next, the method of manufacturing the thermal transfer sheet of thefirst embodiment of the present invention will be explained. The methodof manufacturing the thermal transfer sheet of the first embodiment ischaracterized in that it comprises a colorant layer forming step where acoating liquid for colorant layer is applied onto a surface of asubstrate sheet to form a colorant layer; wherein the coating liquid forcolorant layer used in the colorant layer forming step contains apredetermined solvent, a colorant dispersible in the predeterminedsolvent, a dispersant and a binder resin; wherein the colorantdispersible in the predetermined solvent is dispersed in a particle sizeof not less than 50 nm and not more than 300 nm in the coating liquidfor colorant layer; and, wherein the dispersant is one or more kinds ofdispersants selected from the group consisting of polyether-baseddispersants, graft type polymer dispersants, acryl-based block typepolymer dispersants, urethane-based polymer dispersants and azo-baseddispersants.

(Colorant Layer Forming Step)

As the coating liquid for colorant layer used in the colorant layerforming step, the coating liquid for the colorant layer of the firstembodiment described above can be used as-is, thus the detaileddescription thereof will be omitted here.

There is no particular limitation on the coating method of the coatingliquid for colorant layer, and for instance, it is possible to selectappropriately and use any known method such as gravure coating, rollcoating method, screen printing method, reverse roll coating methodusing a gravure plate, etc. There is no particular limitation on thecoating amount of the coating liquid for colorant layer, but usually, itis in the range of about 0.2 g/m²-about 10 g/m² in terms of solidcontent.

The method of manufacturing a thermal transfer sheet of the firstembodiment may include optional step(s) other than the above colorantlayer forming step. For example, it may include a back face layerforming step that forms the back face on another surface of thesubstrate sheet, a step for forming a back face primer layer between thesubstrate sheet and the back face layer.

<<Method of Manufacturing Thermal Transfer Sheet of the SecondEmbodiment>>

Next, a method of manufacturing a thermal transfer sheet of the secondembodiment of the present invention will be explained, while thesuperiority of the thermal transfer sheet which is manufactured by themanufacturing method of the second embodiment will be referred.

FIG. 4 is a schematic cross-sectional view of a thermal transfer sheetwhich is manufactured by the manufacturing method of the secondembodiment. In the manufacturing method of the second embodiment, acolorant layer 3 is formed on a substrate sheet 2 by using a coatingliquid for colorant layer which contains a predetermined solvent, asublimable dye soluble in the predetermined solvent, a colorantdispersible in the predetermined solvent, and a binder resin. In otherwords, the colorant layer 3 is formed by using a coating liquid whichcontains a binder resin, and wherein a sublimable dye 10 y is dissolvedin the predetermined solvent and a colorant 10 x is dispersed in thepredetermined solvent.

Density of an image formed by thermal transfer recording method isbelieved to be closely related to the thermal migration of thesublimable dye contained in the colorant layer, and thus it is importantto improve the thermal migration of the sublimable dye contained in thecolorant layer in order to prepare the colorant layer capable of forminga high density image. As a method for improving the thermal migration ofthe sublimable dye, a method of forming a colorant layer which uses acoating liquid where a sublimable dye is dissolved in the solvent may beenumerated. According to the colorant layer formed by this method, it ispossible to allow the sublimable dye to present at its molecular levelin the colorant layer, and thus it is possible to improve the thermalmigration of the sublimable dye in the colorant layer. On the otherhand, with respect to a colorant layer formed by using a coating liquidprepared by dispersing the sublimable dye in a solvent in place of thecoating liquid obtained by dissolving the sublimable dye in a solvent,since the sublimable dye presents in its state of having a certaindegree of particle diameter in the colorant layer, the thermal migrationof the sublimable dye is forced to decrease, and it becomes difficult toperform high-density image formation.

As described in the thermal transfer sheet of the first embodiment, inthe case of forming the colorant layer 3C by using the coating liquidprepared by dissolving the sublimable dye 10 y in the predeterminedsolvent (see FIG. 3), it is impossible to prevent the occurrence of thekick and the scumming.

Moreover, in order to prevent localization of the sublimable dye to theinterfaces, the localization being the cause of occurrence of the kickand the scumming, it is preferable to form a colorant layer by using acoating liquid wherein a colorant is dispersed in a solvent. Therefore,in the method of manufacturing the thermal transfer sheet of the firstembodiment as mentioned above, by forming the colorant layer with thecoating liquid for colorant layer which includes a predetermined solventand a colorant dispersible to the predetermined solvent, the occurrencesof the kick and the scumming are repressed. Furthermore, in the methodof manufacturing the thermal transfer sheet of the first embodiment, bycontaining the “specific dispersant(s)” in the coating liquid forcolorant layer, it is plotted to improve the light resistance, and torepress the lowering of the printing density at the highlight portion,while repressing the occurrences of the kick and the scumming.

Incidentally, in order to obtain a colorant layer which can form a highdensity image, while repressing the occurrences of the kick and thescumming, it is preferable to present the colorant at its molecularlevel in the colorant layer. When the colorant layer is formed by usingthe coating liquid for colorant layer where the colorant is dispersed inthe solvent, the colorant 10 x comes to be in a condition of showing acertain degree of the particle diameter in the colorant layer 3. Thus,it is impossible to sufficiently enhance the thermal migration of thecolorant, and it is inferior in the density to the colorant layer whichis formed by using the coating liquid where the sublimable dye 10 y isdissolved in the solvent (See FIG. 3).

Therefore, in order to obtain a thermal transfer sheet capable offorming an image of a higher density, while preventing the occurrencesof the kick and the scumming, the method for manufacturing the thermaltransfer sheet of the second embodiment is characterized in that itcomprises a colorant layer forming step where a coating liquid forcolorant layer is applied onto a surface of a substrate sheet to form acolorant layer; and the coating liquid for colorant layer contains apredetermined solvent, a sublimable dye soluble in the predeterminedsolvent, and a colorant dispersible in the predetermined solvent. Thatis, the method is characterized in that the colorant layer is formed byusing the coating liquid for colorant layer where the sublimable dye isdissolved in the predetermined solvent and the colorant is dispersed inthe predetermined solvent. According to the manufacturing method of thethermal transfer sheet of the second embodiment having this feature, itis possible to manufacture a thermal transfer sheet which is capable offorming a high density image, while preventing the occurrences of thekick and the scumming.

The detailed mechanisms for the aspect that the thermal transfer sheetmanufactured in accordance with the manufacturing method of the secondembodiment plays the above effects have been not clarified well, but thelocalization of the sublimable dye to the interfaces is repressed in thecolorant layer 3 which is formed in accordance with the manufacturingmethod of the second embodiment. Thus, it can be assumed that theoccurrences of the kick and/or the scumming are repressed by thatcondition. Specifically, it can be assumed that the colorant 10 xdispersed in the coating liquid for colorant layer plays a roll ofrepressing the localization of the sublimable dye 10 y to the interfacesof the colorant layer 3, and thus the sublimable dye 10 y can be presentin its dispersed state in the colorant layer 3 which is formed inaccordance with the manufacturing method of the second embodiment.

As a reason why the colorant 10 x dispersed in the coating liquid forcolorant layer plays a roll of repressing the localization of thesublimable dye 10 y dissolved in the coating liquid for colorant to theinterfaces of the colorant layer, the affinity of the sublimable dye 10y with the colorant 10 x can be mentioned. According to the conventionalmethod, when the colorant layer is formed by using a sublimable dye 10 ydissolved in a coating liquid for colorant layer, the sublimable dye 10y comes to be localized toward free boundary (interface) as shown inFIG. 3. However, in the manufacturing method of the second embodiment,since the colorant 10 x is dispersed in the coating liquid for colorantlayer, it is inferred that it is possible to locate the sublimable dye10 around the particles of the colorant 10 x that are present in adispersed state in the colorant layer 3 formed by the manufacturingmethod of the second embodiment, owing to the affinity of the colorant10 x with the sublimable dye 10 y. Thus, as shown in FIG. 4, in thecolorant layer 3 which is formed in accordance with the manufacturingmethod of the second embodiment, it is believed that the localization ofthe sublimable dye 10 y to the interfaces is suppressed, and thus itbecomes possible to allow the sublimable dye 10 y to present in itsdistributed state in the colorant layer 3, and it becomes possible toprevent the occurrences of the kick and/or the scumming.

Further, in the manufacturing method of the second embodiment, since thecolorant layer 3 is formed by using a coating liquid for colorant layerwhere the sublimable dye is dissolved in a solvent, it is possible toallow the sublimable dye to present at its molecular level in thecolorant layer 3. Thus, while preventing the occurrences of the kickand/or the scumming, it is possible to form a high density image.

Even not according to this hypothetical mechanisms, the point that, whenusing the colorant layer which is formed by using the coating liquidwhere the sublimable dye 10 y is dissolved in the predetermined solventand the colorant 10 x is dispersed in the predetermined solvent, itbecomes possible to form a high density image, while repressing theoccurrences of the kick and/or the scumming, is revealed from theresults of Examples and Comparative Examples described later.

Hereinafter, each component used in the manufacturing method of thesecond embodiment, and each component contained in the coating liquidfor colorant layer will be described.

As a substrate sheet used in the manufacturing method of the secondembodiment, the substrate sheet as described in the above explanation ofthe thermal transfer sheet of the first embodiment can be used as-is,and thus, a detailed description thereof will be omitted here.

(Coating Liquid for the Colorant Layer in the Manufacturing Method ofthe Second Embodiment)

The coating liquid for colorant layer used in the manufacturing methodof the second embodiment (hereinafter, it is referred to as “coatingliquid for colorant layer of the second embodiment”) contains a binderresin, a predetermined solvent, a sublimable dye dissolvable in thepredetermined solvent, and a colorant dispersible in the predeterminedsolvent. That is, in the coating liquid for colorant layer of the secondembodiment, the sublimable dye 10 y is present in its dissolved state,and the colorant 10 x is present in its dispersed state.

There is no particular limitation on the binder resin which is includedin the coating liquid for colorant layer of the second embodiment, forexample, it is possible to use the binder resins described in the aboveexplanation of the colorant layer of the thermal transfer sheet of thefirst embodiment as-is, and thus, a detailed description thereof will beomitted here.

The “predetermined solvent” contained in the coating liquid for colorantlayer of the second embodiment means a solvent which is possible todissolve the sublimable dye, and is possible to disperse the colorant.There is no particular limitation for the predetermined solvent, forexample, it is possible to appropriately select one from the solvents asdescribed in the above explanation of the colorant layer of the thermaltransfer sheet of the first embodiment, and use it. Thus, a detaileddescription thereof will be omitted here.

The coating liquid for colorant layer of the second embodiment maycontain one kind of the solvent singly, alternatively, it may containtwo or more solvents. For example, it is possible to use a solvent Acapable of dissolving the sublimable dye in combination with a solvent Bcapable of dispersible the colorant. Here, the case of using the solventA and the solvent B is applicable with the proviso that the solvent Acapable of dissolving the sublimable dye cannot dissolve the colorant.Incidentally, since the sublimable dye is to be dissolved by the solventA, the solvent B may be either capable of or incapable of dissolving thesublimable dye as long as it satisfies the condition that it candisperse the colorant. Further, the coating liquid for colorant layer ofthe second embodiment may further contain solvent(s) other than thesolvent A and the solvent B, provided that at least one colorantcontained in the coating liquid for colorant layer of the secondembodiment is not dissolved in all of the solvent contained in thecoating liquid for colorant layer of the second embodiment.

There is no particular limitation on the “sublimable dye dissolvable inthe predetermined solvent” which is contained in the coating liquid forcolorant layer of the second embodiment, and it can be appropriatelyselected depending on the kind of the predetermined solvent contained inthe coating liquid for colorant layer of the second embodiment.Concretely, as far as the sublimable dye is dissolvable to a solventcontained in the coating liquid for colorant layer of the secondembodiment, any sublimable dye is usable.

There is also no particular limitation on the “colorant dispersible inthe predetermined solvent” which is contained in the coating liquid forcolorant layer of the second embodiment, and it can be appropriatelyselected depending on the kind of the above mentioned predeterminedsolvent contained in the coating liquid for colorant layer of the secondembodiment. Concretely, as far as the colorant is dispersible to asolvent contained in the coating liquid for colorant layer of the secondembodiment, any colorant is usable. Incidentally, the “colorantdispersible to the predetermined solvent” which is contained in thecoating liquid for colorant layer of the second embodiment denotes acolorant which is impossible to be dissolved in the predeterminedsolvent, and there is no particular limitation on the dispersibility ofthe colorant. For instance, it is possible to improve the dispersibilityof the colorant by using the dispersant. That is, as far as the colorantis dispersed in the coating liquid for colorant layer of the secondembodiment as a result, there is no limitation.

The sublimable dye soluble in the predetermined solvent and the colorantdispersible in the predetermined solvent can be appropriately selecteddepending on the solvent contained in the coating liquid for colorantlayer of the second embodiment. Concretely, at first a predeterminedsolvent is selected, and then, a sublimable dye soluble in thepredetermined solvent and a colorant dispersible in the predeterminedsolvent may be selected.

As the sublimable dye and the colorant contained in the coating liquidfor colorant layer of the second embodiment, the sublimable dyes and thecolorants as described in the above explanation for the colorant layerof the thermal transfer sheet of the first embodiment can be used withan appropriate selection, and thus, a detailed description thereof willbe omitted here.

Here, since the quinophthalone dyes represented by the above formula (1)possesses light resistance and a high brightness, they are preferable asthe sublimable dye dissolvable to the predetermined solvent, or thesublimable dye dispersible to the predetermined solvent.

Further, since the pigments represented by the above formula (2) canshow a high dispersibility in the coating liquid for colorant layer ofthe second embodiment, and can increase the stability of the coatingliquid for colorant layer of the second embodiment, and further it canalso prevent the occurrences of the kick and the scumming effectively,they are preferable as the colorant dispersible to the predeterminedsolvent.

The coating liquid for colorant layer of the second embodiment maycontain, as the “sublimable dye dissolvable in the predeterminedsolvent”, a kind of the sublimable dye singly, or two or more kind ofthe sublimable dyes in combination. Further, in the case that the“colorant dispersible to the predetermined solvent” is a sublimable dye,the coating liquid for colorant layer of the second embodiment maycontain, as the “sublimable dye dispersible in the predeterminedsolvent”, a kind of the sublimable dye singly, or two or more kind ofthe sublimable dyes in combination. It is also possible to contain, asthe “colorant dispersible to the predetermined solvent”, sublimabledye(s) and pigment(s) in combination. It is also possible to use two ormore kinds of pigments in combination. With respect to the pigment, itis possible to use the pigments as described in the above explanationfor the colorant layer of the thermal transfer sheet of the firstembodiment with an appropriate selection, and thus, the detaileddescription thereof will be omitted here.

Hereinafter, examples of the colorant(s) and the sublimable dye(s)contained in the coating liquid for colorant layer of the secondembodiment will be explained with referring to concrete solvents. Themanufacturing method of the thermal transfer sheet of the secondembodiment is not limited to these combinations.

In the case that the predetermined solvent is a mixed solvent of methylethyl ketone/toluene:

As the sublimable dye capable of dissolving in the mixed solvent ofmethyl ethyl ketone/toluene, for example, Disperse Yellow 201 or thelike can be used. Further, as the colorant dispersible in the mixedsolvent of methyl ethyl ketone/toluene, for instance, the pigmentsexemplified above, the sublimable dyes exemplified above, for example,Disperse Yellow 54 or the like can be used.

In the coating liquid for colorant layer, a dispersant for improving thedispersibility of the colorant may be contained. As the dispersant, forinstance, graft-type polymer dispersion aids, polyether-based dispersantaids, acryl based block type polymer dispersant aids and the like may beenumerated. In addition, as the dispersant, derivatives in which organicpigment was treated with a sulfonated compound or the like may beenumerated. As the treating method, in addition to rosin treatment,surface treatments such as acidic group treatment, basic treatment,pigment derivative treatment, and the like may be enumerated.

Further, the coating liquid for colorant layer may contain otheroptional additives, for instance, a releasing agent for improvingreleasability from the receiving layer of the thermal transfer-imagereceiving sheet, an antistatic agent, an organic or inorganic filler forcontrolling the lubricity with the receiving layer, etc., in addition tothe essential components, i.e., the binder resin, the predeterminedsolvent, the sublimable dye dissolvable in the predetermined solvent,and the colorant dispersible to the predetermined solvent.

In a preferred method for manufacturing a thermal transfer sheet of thesecond embodiment, the coating liquid for colorant layer of the secondembodiment contains the “specific dispersant(s)” as described in theabove explanation for the coating liquid for colorant layer of the firstembodiment, in addition to the binder resin, the predetermined solvent,the colorant 10 x dispersible to the predetermined solvent and thesublimable dye dissolvable in the predetermined solvent. According tothis manufacturing method of the thermal transfer sheet of thispreferred form, owing to the function of the “specific dispersants”, itis possible to further repress the occurrences of the kick and thescumming, and further improve the density of the image formed, in thethermal transfer sheet manufactured by the manufacturing method of thesecond embodiment, and further, it is also possible to further improvethe light resistance, and suppress the reduction of the print density inthe highlight portion.

Although there is no particular limitation for the method of forming thecolorant layer 3, and for instance, the colorant layer can be formed bypreparing a coating liquid for colorant layer where a binder resin, asolvent, a sublimable dye dissolvable in the solvent, and a colorantdispersible to the solvent, and optionally any additive(s) such as adispersant, a releasing agent or the like as necessary, are used, andthe sublimable dye is dissolved in the solvent and the colorant isdispersed in the solvent, coating thus prepared coating liquid forcolorant layer on the substrate sheet in accordance with a known coatingprocedure such as the gravure printing method, the screen printingmethod, the reverse roll coating printing method using a gravure plate,or the like, and then drying the coated solution. Although there is noparticular limitation about the coating amount of the coating liquid forthe colorant layer, it is preferable that it is in the range of 0.2g/m²-10 g/m² in terms of solid content.

As described above, the manufacturing method of the second embodiment isfairly explained as mainly describing about the manufacturing method forproviding the colorant layer 3 directly on the substrate sheet 2.Similar to the method of manufacturing a thermal transfer sheet of thefirst embodiment, however, the manufacturing method of the secondembodiment may include step(s) of providing arbitrary layer(s), betweenthe substrate sheet 2 and the colorant layer 3, and/or on anothersurface side of the substrate sheet 2, on which the colorant layer 3does not formed.

<Thermal Transfer Sheet of the Second Embodiment>

The thermal transfer sheet 1 of the second embodiment, as shown in FIG.1, takes a configuration in which the colorant layer 3 is provided onthe substrate sheet 2. Here, w the thermal transfer sheet 1 of thesecond embodiment is characterized in that, as shown in FIG. 4, thecolorant layer 3 includes a predetermined solvent, a sublimable dye 10y, and a colorant 10 x, and the sublimable dye 10 y is a sublimable dyethat is soluble in the predetermined solvent, and the colorant 10 x is acolorant that is dispersible in the predetermined solvent.

According to the thermal transfer sheet of the second embodimentcomprising the colorant layer 3 having the above characteristics, forthe reasons as described in the above explanation for the manufacturingmethod of the second embodiment, it is possible to prevent theoccurrences of the kick and/or the scumming, and to form a high densityimage.

Here, it should be noted that, although the thermal transfer sheet ofthe second embodiment also has an essential condition that the colorantlayer 3 contains a predetermined solvent, the condition does not intendto denote that the predetermined solvent is positively and activelycontained in the colorant layer 3. But, the predetermined solventcontained in the colorant layer 3 refers to a residual solvent containedin the colorant layer 3. Concretely, when the solvent remaining in thecolorant layer 3 is a solvent which can dissolve the sublimable dyeincluded in the colorant layer and which can disperse the colorantincluded in the colorant layer, it can be said that the thermal transfersheet of the second embodiment can exhibit the same functions andeffects as the thermal transfer sheet manufactured by the manufacturingmethod of the second embodiment.

“Determination Method for Colorant, Residual Solvent”

For instance, by the following method, it is possible to determinewhether a thermal transfer sheet of interest (hereinafter, referred toas target thermal transfer sheet) satisfies the matters specifying thethermal transfer sheet of the second embodiment or not. First, thecolorant layer of the target thermal transfer sheet is analyzed in orderto identify the colorant component contained in the colorant layer. Asthe identification method of the colorant components, any conventionallyknown analytical method such as the nuclear magnetic resonancespectroscopy, IR spectroscopy or the like is applicable.

In the above analysis of the colorant layer, when it is determined thatthe colorant contained in the colorant layer is only one kind, thetarget thermal transfer sheet can be judged as not being satisfying thematters specifying the thermal transfer sheet of the second embodiment.On the other hand, when it is determined that the colorants contained inthe colorant layer are two or more kinds, the kind of the solventremaining in the colorant layer is further determined. As theidentification method of the kind of the solvent, for example, the gaschromatography is applicable. In the identification of the kind of thesolvent by the gas chromatography, for instance, a gas chromatographyanalyzer such as Gas Chromatography GC14-A, manufactured by ShimadzuCorporation, and the like can be utilized. Incidentally, in order toeliminate the influence of the solvents which have been contained in thesubstrate sheet, a heat resisting sliding layer, and/or any arbitrarylayers in the target thermal transfer sheet, it is necessary to analyzeto the layer corresponding to the colorant layer of the target thermaltransfer sheet on the identification of the kind of the solvent.Concretely, when the kind of the solvent remaining in the colorant layeris determined by using the gas chromatography method, it is important totake only a part of the layer corresponding to the colorant layer of thetarget thermal transfer sheet and carry out the analyze to the portion.

When at least one of the identified colorant components as mentionedabove is the colorant component dissolvable in the identified solvent asmentioned above, and at least one of the identified colorant componentsas mentioned above is the colorant component dispersible in theidentified solvent as mentioned above, the target thermal transfer sheetcan be judged as being satisfying the matters specifying the thermaltransfer sheet of this embodiment. Incidentally, in the case that two ormore kinds of solvents are identified in the colorant layer of thetarget thermal transfer sheet, when at least one of the identifiedcolorant components is the colorant component dissolvable in at leastone of the identified solvents, and at least one of the identifiedcolorant components is the colorant component dissolvable to none of theidentified solvents, the target thermal transfer sheet can be judged asbeing satisfying the matters specifying the thermal transfer sheet ofthis embodiment. Further, by using the “determination method fordispersibility of colorant to predetermined solvent” as described in theabove explanation for the manufacturing method of the first embodiment,it is possible to determine whether the identified colorant can bedissolved or can be dispersed in the identified solvent.

Hereinafter, each component of the thermal transfer sheet of the secondembodiment will be described. Incidentally, the thermal transfer sheetof the second embodiment is correlated with the manufacturing method ofthe second embodiment, and thus, unless otherwise specified, thosedescribed in the manufacturing method of the second embodiment can beused as-is.

There is no particular limitation on the substrate sheet 2, and it ispossible to use any of the substrate sheets described in themanufacturing method of the second embodiment by selectingappropriately.

(Colorant Layer)

In the colorant layer 3, a binder resin, a sublimable dye, a colorantand a predetermined solvent are included. With respect to eachindividual component, it is possible to use any of the correspondingcomponents described in the manufacturing method of the secondembodiment by selecting appropriately. Herein, the sublimable dyereferred to in the thermal transfer sheet of the second embodiment meansa sublimable dye dissolvable in a predetermined solvent, and thecolorant means a colorant dispersible in the predetermined solvent.

With respect to the containing ratio of the sublimable dye and thecolorant in the colorant layer, there is no particular limitation, andthe ratio can be determined appropriately depending on the function(s)required to the colorant layer, for instance, light resistance, densitycharacteristics, etc.

In a preferred form, the colorant layer 3 further contains the “specificdispersant(s)” as described in the above explanation for the firstembodiment. According to this colorant layer 3, it is possible torepress the occurrences of the kick and the scumming, and furtherimprove the density of the image formed, and further, it is alsopossible to further improve the light resistance, and suppress thereduction of the print density in the highlight portion, owing to thefunction of the “specific dispersant(s)”.

The colorant layer 3 may also contain optional components such as areleasing agent. For example, by containing a releasing agent in thecolorant layer 3, it is possible to improve the releasing propertybetween the colorant layer 3 and the receiving layer at the time ofimage formation. In the case that measures for releasing property istaken in the receiving layer side, it is not always necessary to includethe releasing agent in the colorant layer 3.

As the releasing agent, it is possible to use the releasing agents asdescribed in the above explanation for the manufacturing method of thefirst embodiment with an appropriate selection, and thus, the detaileddescription thereof will be omitted here.

Further, a primer layer may be provided between the substrate sheet 2and the colorant layer 3. As the primer layer, the primer layer asdescribed in the above explanation for the thermal transfer sheet of thefirst embodiment can be used as-is, and thus, the detailed descriptionthereof will be omitted here.

(Back Face Layer)

Further, a back face layer may be provided on the other surface of thesubstrate sheet 2. As the back face layer, the back face layer asdescribed in the above explanation for the thermal transfer sheet of thefirst embodiment can be used as-is, and thus, the detailed descriptionthereof will be omitted here.

(Back Face Primer Layer)

Further, a back face primer layer may be provided between the substratesheet 2 and the back face layer 5. As the back face primer layer, theback face primer layer as described in the above explanation for thethermal transfer sheet of the first embodiment can be used as-is, andthus, the detailed description thereof will be omitted here.

<Method of Manufacturing a Thermal Transfer Sheet of Third Embodiment>

Next, a thermal transfer sheet which is manufactured by a method formanufacturing a thermal transfer sheet of the third embodiment will beexplained with reference to FIG. 5. FIG. 5 is a schematiccross-sectional view of the thermal transfer sheet which is manufacturedby the method for manufacturing a thermal transfer sheet of the thirdembodiment.

The method for manufacturing a thermal transfer sheet of the thirdembodiment is characterized by comprising a first colorant layer formingstep where a coating liquid which contains a first solvent and asublimable dye soluble in the first solvent is applied onto a surface ofa substrate sheet to form the first colorant layer; and a secondcolorant layer forming step where a coating liquid which contains asecond solvent and a colorant dispersible in the second solvent isapplied onto the first colorant layer to form the second colorant layer.

In the third embodiment, on the substrate sheet, the first colorantlayer 3A is formed by coating a coating liquid which contains a firstsolvent and a sublimable dye soluble in the first solvent. As explainedabove, in the colorant layer formed by using the coating liquid whereinthe sublimable dye is dissolved, the sublimable dye is present in astate of being localized to the interfaces (See, FIG. 3), and is in astate of causing the kick and/or the scumming with ease. In other words,in the case that a thermal transfer sheet where only the first colorantlayer 3A is provided on the substrate sheet 2 is manufactured, it isimpossible to prevent the kick and/or the scumming, although it becomespossible to form a high density image by using the thermal transfersheet.

Therefore, in the third embodiment, the occurrences of the kick and/orthe scumming for which the first colorant layer 3A cannot compensate isprevented by forming another layer on the first colorant layer 3A.Concretely, in the third embodiment, a second colorant layer is formedon the first colorant layer by coating a coating liquid which contains asecond solvent and a colorant dispersible in the second solvent onto thefirst colorant layer 3A. Since the second colorant layer 3B provided inthe third embodiment is formed by using the coating liquid where thecolorant is dispersed, the colorant 10 x in the second colorant layer 3Bthus formed (See FIG. 2) are uniformly dispersed, and it is possible toprevent the occurrences of the kick and the scumming owing to thepresence of the second colorant layer 3B. That is, the second colorantlayer 3B is mainly serves just as a lid for closing the sublimable dye10 y localized at the interfaces of the first colorant layer 3A.

Moreover, since the first colorant layer 3A is formed between thesubstrate sheet 2 and the second colorant layer 3B, by using the coatingliquid where the sublimable dye has been dissolved, the sublimable dyecan be present at its molecular in the first colorant layer 3A. Thus, itis possible to enhance the thermal migration of the sublimable dyecontained in the first colorant layer 3A, and also possible to foam ahigh density image. Furthermore, since the second colorant layer 3Bcontains the colorant 10 x, owing to the synergistic effect of thesublimable dye 10 y with the colorant 10 x, it becomes possible to forma higher density image.

Next, the coating liquid for forming the first colorant layer 3A, andthe coating liquid for forming the second colorant layer 3B will bedescribed. Hereinafter, the coating liquid for forming the firstcolorant layer 3A is referred to as “first coating liquid” and thecoating liquid for forming the second colorant layer 3B is referred toas “second coating liquid” for these explanations.

(First Coating Liquid)

In the first coating liquid, a first binder resin, a first solvent, anda sublimable dye dissolvable to the first solvent are included. That is,the sublimable dye is present in a state of being dissolved in the firstcoating liquid.

There is no particular limitation for the first binder resin containedin the first coating liquid, and it can be appropriately selecteddepending on the kind of the sublimable dye dissolvable in a firstsolvent. For example, the binder resins contained in the coating liquidfor the colorant layer as described in the manufacturing method of thefirst embodiment may be mentioned. Ditto for the second binder resinwhich is contained in the second coating liquid described below. Also,the first binder resin may be the same with or may be different from thesecond binder resin.

“Sublimable Dye”

There is no particular limitation on the sublimable dye which isdissolved in the first coating liquid, and it can be appropriatelyselected depending on the kind of the first solvent to be contained inthe first coating liquid. For example, the sublimable dyes as describedin the above explanation for the manufacturing method of the firstembodiment may be mentioned. The first coating liquid may contain two ormore kinds of the sublimable dyes.

“First Solvent”

As the first solvent, as long as it is capable of dissolving thesublimable dye, it is not particularly limited, and it may beappropriately selected from known solvents. The first coating liquid maycontain two or more solvents, provided that at least one of the solventsis capable of dissolving at least one of the sublimable dyes containedin the first coating liquid.

In the first coating liquid, colorant(s) dispersible to the firstsolvent may be contained. That is, the first colorant layer 3A may havea same constitution as the colorant layer 3 (See FIG. 5) which is formedby the manufacturing method of the above mentioned second embodiment.Further, in the first coating liquid, any optional ingredient(s) may becontained, in addition to the first binder resin, the first solvent, andthe sublimable dye.

Although there is no particular limitation on the method of forming thefirst colorant layer, and for instance, the first colorant layer can beformed by preparing a first coating liquid where a sublimable dye isdissolved in the solvent, coating thus prepared first coating liquid onthe substrate sheet in accordance with a known coating procedure such asthe gravure printing method, the screen printing method, the reverseroll coating printing method using a gravure plate, or the like, andthen drying the coated solution. Although there is no particularlimitation about the coating amount of the first coating liquid, it ispreferable that it is in the range of 0.1 g/m²-5 g/m² in terms of solidcontent.

(Second Coating Liquid)

In the second coating liquid, a second binder resin, a second solvent,and a colorant dispersible to the second solvent are included. That is,the colorant is present in a state of being dispersed in the secondcoating liquid.

“Colorant”

There is no particular limitation on the colorant which is dispersed inthe second coating liquid, and it can be appropriately selecteddepending on the kind of the second solvent to be contained in thesecond coating liquid. The colorant may be sublimable dye(s), or may bepigments, and it is possible to use any of the colorants as described inthe above explanation for the manufacturing method of the firstembodiment. The second coating liquid may contain two or more kinds ofcolorants.

“Second Solvent”

As the second solvent, as long as it is capable of dispersing thecolorant as mentioned above, it is not particularly limited, and it maybe appropriately selected from known solvents. The first coating liquidmay contain two or more solvents, provided that at least one of thecolorants contained in the second coating liquid can be dissolved innone of the solvents contained in the first coating liquid.

In the second coating liquid, any optional ingredient (s) may becontained, in addition to the second binder resin, the second solvent,and the dispersible colorant. For example, the second coating liquid maycontain a dispersant for improving the dispersibility of the colorant.As the dispersant, for example, it is possible to use the dispersants asdescribed in the thermal transfer sheet of the first embodiment.

Further, in the second coating liquid, a sublimable dye dissolvable inthe second solvent to be contained in the second coating liquid maycontained. That is, the second colorant layer 3B may have a sameconstitution as the colorant layer 3 (See FIG. 4) which is formed by themanufacturing method of the above mentioned second embodiment. Accordingto this constitution, since the sublimable dye(s) is dissolved in bothof the first coating liquid and the second coating liquid, it can beexpected to form a higher density image, by means of the synergisticeffect of the first colorant layer 3A and the second colorant layer 3B.

In the case that the second colorant layer 3B which is formed using thesecond coating liquid is located at the outermost surface of the thermaltransfer sheet, it is preferable that a releasing agent is contained inthe second coating liquid. As the releasing agent, the releasing agentsas described in the explanation of the colorant layer of the thermaltransfer sheet of the first embodiment may be used. Incidentally, in thecase that measures for improving the releasing property is taken in thetransfer receiving article side, for instance, the receiving layer sideof the thermal transfer image-receiving sheet, it is not alwaysnecessary to include the releasing agent in the second coating liquid.

As described above, the first solvent and the sublimable dye dissolvableto the first solvent which are contained in the first coating liquid, aswell as the second solvent and the colorant dispersible to the secondsolvent which are contained in the second solvent, in accordance withthe method of manufacturing the thermal transfer sheet of the thirdembodiment are fairly explained. The first solvent and the secondsolvent may be different from each other, and the sublimable dyecontained in the first coating liquid and the colorant contained in thesecond coating liquid may be also different from each other.Alternatively, the first solvent and the second solvent may be the samewith each other, and the sublimable dye contained in the first coatingliquid and the colorant contained in the second coating liquid may bealso different from each other. In this case, at least one kind of thesublimable dyes included in the first coating liquid should be dissolvedin the common solvent, and at least one kind of the colorants includedin the second coating liquid should be dispersed in the common solvent

In further another instance, the first solvent and the second solventmay be different from each other, and the sublimable dye contained inthe first coating liquid and the colorant contained in the secondcoating liquid may be the same with each other. In this case, the firstsolvent contained in the first coating liquid should be able to dissolvethe common colorant, and the second solvent contained in the secondcoating liquid and being different from the first solvent should be ableto disperse the common colorant.

In a preferred method for manufacturing a thermal transfer sheet of thethird embodiment, the second coating liquid further contains the“specific dispersant(s)” as described in the above explanation for thecoating liquid for colorant layer of the first embodiment, in additionto the binder resin, the predetermined solvent, and the colorant 10 xdispersible to the predetermined solvent. According to the manufacturingmethod of the thermal transfer sheet of this preferred form, it ispossible to repress the occurrences of the kick and the scumming in thethermal transfer sheet obtained by the manufacturing method of the thirdembodiment, and further improve the density of the image formed, andfurther, it is also possible to further improve the light resistance,and suppress the reduction of the print density in the highlightportion, owing to the function of the “specific dispersant(s)”.

Although there is no particular limitation on the method of forming thesecond colorant layer, and for instance, the second colorant layer canbe formed by preparing a second coating liquid where a colorant isdispersed in the solvent, coating thus prepared second coating liquid onthe first colorant layer in accordance with a known coating proceduresuch as the gravure printing method, the screen printing method, thereverse roll coating printing method using a gravure plate, or the like,and then drying the coated solution. Although there is no particularlimitation about the coating amount of the second coating liquid, it ispreferable that it is in the range of 0.1 g/m²-5 g/m² in terms of solidcontent.

As described above, the manufacturing method of the third embodiment isfairly explained as mainly describing about the manufacturing method forproviding the second colorant layer 3B directly on the first colorantlayer 3A. However, the manufacturing method of the third embodiment mayinclude step(s) of providing arbitrary layer(s) between the firstcolorant layer 3A and the second colorant layer 3B. Further, themanufacturing method of the third embodiment may include step(s) ofproviding arbitrary layer(s) between the substrate sheet 2 and the firstcolorant layer 3A. In addition, it may include step(s) of providingarbitrary layer(s) on another surface side of the substrate sheet 2, onwhich the first colorant layer 3A does not formed.

<Thermal Transfer Sheet of Third Embodiment>

The thermal transfer sheet 1 of the third embodiment is characterized inthat it comprises a substrate 2 and a colorant layer 3 provided on onesurface of the substrate sheet 3, as shown in FIG. 5; wherein thecolorant layer 3 comprises a layered structure in which a first colorantlayer 3A and a second colorant layer 3B are layered in this order;wherein the first colorant layer 3A contains a first solvent and asublimable dye soluble in the first solvent; and wherein the secondcolorant layer contains a second solvent and a colorant dispersible inthe second solvent.

According to the thermal transfer sheet of the third embodiment havingthe colorant layer 3 of the above features, since the second colorantlayer 3B is serves just as a lid for closing the sublimable dye 10 ylocalized at the interfaces of the first colorant layer 3A, and by thesame reasons with those explained in the method for manufacturing thethermal transfer sheet of the third embodiment, it is possible toprevent the occurrences of the kick and the scumming, and to form a highdensity image.

Here, it should be noted that, although the thermal transfer sheet ofthe third embodiment also has an essential condition that the firstcolorant layer 3A contains a first solvent and the second colorant layer3B contains a second solvent, as is the case with the thermal transfersheet of the first embodiment or the second embodiment, the conditionsdoes not intend to denote that the first and second solvents arepositively and actively contained in the first colorant layer 3A and thesecond colorant layer, respectively. But, the first solvent contained inthe first colorant layer 3A refers to residual solvent contained in thefirst colorant layer 3A, and the second solvent contained in the secondcolorant layer 3B refers to residual solvent contained in the secondcolorant layer 3B. Concretely, when the solvent remaining in the firstcolorant layer 3A is a first solvent which can dissolve the sublimabledye included in the first colorant layer and the solvent remaining inthe second colorant layer 3B is a second solvent which can disperse thecolorant included in the second colorant layer, it can be said that thethermal transfer sheet of the third embodiment can exhibit the samefunctions and effects as the thermal transfer sheet manufactured by themanufacturing method of the third embodiment.

As long as the dissolving and dispersing conditions for the sublimabledye in the first colorant layer 3A and the colorant in the secondcolorant layer 3B can satisfy the above mentioned relation, as describedin the manufacturing method of the third embodiment, the first solventremained in the first colorant layer and the second solvent remained inthe second colorant layer may be the same with each other. In this case,the first colorant layer 3A should contain at least one kind of thesublimable dye which is soluble in the common solvent, and also, thesecond colorant layer should contain at least one kind of the colorantwhich is dispersible in the common solvent. Alternatively, thesublimable dye contained in the first colorant layer 3A and the colorantcontained in the second colorant layer may be the same with each otherIn this case, a first solvent capable of dissolving the common colorantshould be remained in the first colorant layer 3A, and a second solventcapable of dispersing the common colorant should be remained in thesecond colorant layer 3B.

It is possible to determine whether a thermal transfer sheet of interestsatisfies the matters specifying the thermal transfer sheet of the thirdembodiment or not, by investigating the relations of the solvents andthe colorants contained in the individual layers. Concretely, when thecolorant layer in the target thermal transfer sheet does not have alayered structure, the target thermal transfer sheet can be judged asnot being satisfying the matters specifying the thermal transfer sheetof the third embodiment. On the other hand, when the colorant layer ofthe target thermal transfer sheet can be determined as to have a layeredstructure, solvent(s) and colorant(s) contained in the colorant layercloser to the substrate sheet are identified. On this identification,when the colorant component is the one which can be dissolved in theidentified solvent, the colorant layer can be judged as being satisfyingthe construction of the first colorant layer. Then, solvent(s) andcolorant(s) contained in the colorant layer farther from the substratesheet are identified. On this identification, when the colorantcomponent is the one which can be dispersed in the identified solvent,the colorant layer can be judged as being satisfying the construction ofthe second colorant layer. Further, when a layer of the sameconstruction as the first colorant layer and a layer of the sameconstruction as the second colorant layer are layered, the target heattransfer sheet can be judged as being satisfying the matters specifyingthe thermal transfer sheet of the third embodiment. As the determinationmethod for colorant and solvent, the methods as described in theexplanation for the first embodiment can be used as-is. Further, byusing the “determination method for dispersibility of colorant topredetermined solvent” as described in the above explanation for themanufacturing method of the first embodiment, it is possible todetermine whether the identified colorant can be dissolved or can bedispersed in the identified solvent.

Next, each component of the thermal transfer sheet of the thirdembodiment will be described. Incidentally, the thermal transfer sheetof the third embodiment is correlated with the manufacturing method ofthe third embodiment, and thus, unless otherwise specified, thosedescribed in the manufacturing method of the third embodiment can beused as-is.

There is no particular limitation on the substrate sheet 2, and it ispossible to use any of the substrate sheets described in themanufacturing method of the first embodiment by selecting appropriately.

(First Colorant Layer)

In the first colorant layer 3A, a first binder resin, a first solvent,and a sublimable dye dissolvable to the first solvent are included. Withrespect to each individual component, it is possible to use any of thecorresponding components described in the above explanation for thefirst coating liquid of the manufacturing method of the third embodimentby selecting appropriately.

The first colorant layer may contain a colorant dispersible in the firstsolvent. The first colorant layer 3A may any optional component(s) whichare described in the above explanation for the first coating liquid ofthe manufacturing method of the third embodiment, in addition to thefirst binder resin, the first solvent, the sublimable dye dissolvable tothe first solvent.

With respect to the method for forming the first colorant layer 3A, itis possible to use the method as described in the manufacturing methodof the third embodiment. Ditto for the second coloring layer 3B.

(Second Colorant Layer)

In the second colorant layer 3B, a second binder resin, a secondsolvent, and a colorant dispersible to the second solvent are included.With respect to each individual component, it is possible to use any ofthe corresponding components described in the above explanation for thesecond coating liquid of the manufacturing method of the thirdembodiment by selecting appropriately.

The second colorant layer 3B may contain a colorant dissolvable in thesecond solvent. The second colorant layer 3B may any optionalcomponent(s) which are described in the above explanation for the secondcoating liquid of the manufacturing method of the third embodiment, inaddition to the second binder resin, the second solvent, the colorantdispersible to the first solvent.

The second colorant layer of a preferred mode may further contain the“specific dispersant(s)” as described in the above explanation for thecoating liquid for colorant layer of the first embodiment. According tothe thermal transfer sheet which having this second colorant layer 3B,it is possible to repress the occurrences of the kick and the scummingin the thermal transfer sheet, and further improve the density of theimage formed, and further, it is also possible to further improve thelight resistance, and suppress the reduction of the print density in thehighlight portion, owing to the function of the “specificdispersant(s)”.

The thermal transfer sheet of the third embodiment, as is the same withthe thermal transfer sheet of the first embodiment, may have a primerlayer between the substrate sheet 2 and the first colorant layer 3A, andmay have a back face layer on another surface of the substrate sheet 2.Further, a back face primer layer may be provided between the substratesheet 2 and the back face layer.

<<Image Forming Method>>

Next, the image forming method of an embodiment of the present inventionwill be described.

The image forming method of the first embodiment is characterized inthat it is for forming image on a thermal transfer image-receiving sheetby using a thermal transfer sheet having a colorant layer on a surfaceof a substrate sheet in combination with the thermal transferimage-receiving sheet having a receiving layer on a surface of anothersubstrate sheet; wherein the colorant layer of the thermal transfersheet contains a predetermined solvent, a colorant dispersible in thepredetermined solvent, a dispersant and a binder resin; and wherein thedispersant is one or more kinds of dispersants selected from the groupconsisting of polyether-based dispersants, graft type polymerdispersants, acryl-based block type polymer dispersants, urethane-basedpolymer dispersants and azo-based dispersants. That is, it ischaracterized by using the thermal transfer sheet of the firstembodiment as the thermal transfer sheet.

The image forming method of the second embodiment is characterized byusing the thermal transfer sheet of the second embodiment as the thermaltransfer sheet. The image forming method of the third embodiment ischaracterized by using the thermal transfer sheet of the thirdembodiment as the thermal transfer sheet.

According to the image forming methods of the first embodiment, thesecond embodiment, and the third embodiment, of the present invention,it is possible to form a photographic tone color image of high qualitywith a continuous tone image by sublimation transfer.

(Thermal Transfer Image-Receiving Sheet)

The thermal transfer image-receiving sheet to be used in combinationwith the above thermal transfer sheet has another substrate sheet and areceiving layer provided on the another substrate sheet as essentialcomponents. As the another substrate sheet used herein, it is possibleto use the same type with the substrate sheet of the above mentionedthermal transfer sheet. Alternatively, it is also possible to use adifferent type from the substrate sheet of the above mentioned thermaltransfer sheet. The thermal transfer image-receiving sheet may be anyone provided with this constitution, without any limitation. It can beselected from any conventionally known thermal transfer image-receivingsheets as appropriate to be used it.

(Image Formation)

With respect to the image forming method of the present invention, aslong as the condition that the thermal transfer sheet to be used for theimage formation is one of the thermal transfer sheet of the firstembodiment, the thermal transfer sheet of the second embodiment and thethermal transfer sheet of the third embodiment as described above issatisfied, there are no particular restrictions for other requirements.For example, The image can be formed by superposing the colorant layerof the thermal transfer sheet to the receiving layer of the thermaltransfer image-receiving sheet, then applying heat from the back side ofthe thermal transfer sheet with by a heating means such as a thermalhead in order to transfer the colorant contained in the colorant layerto the receiving layer side.

EXAMPLE

Next, the present invention will be described with referring toExamples. Hereinafter, the expressions of “part(s)” and “%” are based on“weight”, unless otherwise especially mentioned.

Example 1

In accordance with the procedure described below, a coating liquid forcolorant layer and a thermal transfer sheet were prepared.

(Preparation of Coating Liquid for Colorant Layer 1)

As the following composition, a coating liquid for colorant layer 1 wasprepared by adding a colorant, a dispersant, a binder resin, a solventand 250 parts by weight of zirconia beads having a particle diameter of2.0 mm into a glass bottle, sealing the glass bottle, shaking thecontent with a paint shaker (manufactured by Asada Iron Works Co., Ltd.)for 1 hour as a preliminary crushing, then removing the above mentionedzirconia beads from the bottle and adding 250 parts by weight ofzirconia beads having a particle diameter of 0.1 mm to the bottle, anddispersing the content with the paint shaker similarly for 24 hour as amain crushing, in order to prepare a coating liquid for colorant layer1. Preparation of the following coating liquids for colorant layer 2-7and 10 were carried out in the same manner an mentioned above.

The point whether the following each individual colorant to be containedin the coating liquid for colorant layer can be solved in a mixedsolvent of toluene and methyl ethyl ketone or can be dispersed in thismixed solvent was determined in advance by the following method. Namely,the method was performed by using toluene/methyl ethyl ketone=1/1 mixedsolvent, adding the colorant into the mixed solvent so as to obtain acolorant concentration of 2 w/v %, then, stirring for one hour withheating to 50° C. Then, the resultant solution was allowed to leftstanding for 60 hours at 25° C., and after the standing, it was observedvisually whether the precipitation or deposition of the colorant iscaused or not. As a result of this observation, if no precipitation ordeposition of the colorant was observed, the colorant was determined asthe soluble colorant, whereas if precipitation or deposition of thecolorant was observed, the colorant was determined as the dispersiblecolorant.

According to the above determination method, the “C. I. Disperse Yellow54” which was to be included in the coating liquids for the colorantlayers was determined to be a dispersible colorant in the toluene/methylethyl ketone mixed solvent. The “sulfonated derivative of C. I. PigmentYellow 138” represented by the above Formula 3, was determined to be adispersible colorant (pigment) in the toluene/methyl ethyl ketone mixedsolvent, in addition to having the function as a dispersant forimproving the dispersibility of the “C. I. Disperse Yellow 54”. Further,the “C. I. Disperse Yellow 201”, and the colorants represented by thefollowing formulae 4 and were determined to be soluble colorants.

<Coating Liquid for Colorant Layer 1>

C.I. Disperse Yellow 54 (it is referred to as “dye A”) 4.75 partsDispersant of poly allyl amine-based graft type polymer 1.75 parts(Ajisper PB881, Mw: 40000-50000, manufactured by Ajinomoto Fine-TechnoCo., Ltd.) Polyvinyl acetal resin 2.05 parts (KS-5, manufactured bySekisui Chemical Co., Ltd.) Methyl ethyl ketone 32.25 parts  Toluene32.25 parts 

The chemical formula of dye A is shown below.

(Preparation of Thermal Transfer Sheet)

As a substrate, polyethylene terephthalate (PET) film which had 4.5 μmin thickness was used. On this substrate, a coating liquid for primerlayer having the following composition was coated so as to obtain acoating amount of solid content of 0.05 g/m² in accordance with the wirebar coating method, and then the coated liquid was dried to form aprimer layer.

<Coating Liquid for Primer Layer>

Alumina sol (average primary particle diameter: 10 × 100 nm 30 parts(solid content: 10%) (Alumina sol 200, manufactured by Nissan ChemicalIndustries Co., Ltd.) Polyvinyl pyrrolidone resin  3 parts (K-90,manufactured by ISP) Water 50 parts Isopropyl alcohol 17 parts

Subsequently, the above mentioned coating liquid for colorant layer 1was coated on the primer layer so as to obtain a coating amount of solidcontent of 0.8 g/m² in accordance with the wire bar coating method, andthen the coated liquid was dried at 80° C. for 2 minutes to form thecolorant layer. Thus, the thermal transfer sheet was prepared.Incidentally, on another surface of this substrate, a coating liquid forback face layer 1 having the following composition was coated so as toobtain a coating amount of solid content of 1.0 g/m² and then the coatedliquid was dried to form a back face layer in advance.

<Coating Liquid for Back Face Layer 1>

Polyvinyl acetal resin 4.55 parts (S-LEC BX-1, manufactured by SekisuiChemical Co., Ltd.) Polyisocyanate 21.0 parts (BURNOCK D750-45, solidcontent: 45% by weight, manufactured by DIC Corporation) Phosphate-basedsurfactant  3.0 parts (PLYSURF A-208N, manufactured by Dai-ichi KogyoSeiyaku Co., Ltd.) Talc 0.7 part (MICRO ACE P-3, manufactured by NipponTalc Co., Ltd.) methyl ethyl ketone 100.0 parts  toluene 100.0 parts 

Example 2

A thermal transfer sheet of Example 2 was obtained by carrying out thesame procedure as in Example 1 except that a coating liquid for colorantlayer 2 wherein 1.7 parts of a polyether type dispersant (Solsperse20000, weight average molecular weight: 1900, manufactured by TheLubrizol Corporation) was used instead of 1.7 parts of the poly allylamine-based graft polymer dispersant in the composition of the coatingliquid for colorant layer 1 was used in place of the coating liquid forcolorant layer 1.

Example 3

A thermal transfer sheet of Example 3 was obtained by carrying out thesame procedure as in Example 1 except that a coating liquid for colorantlayer 3 wherein 2.83 parts (solid content: 1.7 parts) of an acryl-basedblock type polymer dispersant (BYK-LPN6919, weight average molecularweight: 9000, solid content: 60%, manufactured by BYK Additives &Instruments) was used instead of 1.7 parts of the poly allyl amine-basedgraft polymer dispersant in the composition of the coating liquid forcolorant layer 1 was used in place of the coating liquid for colorantlayer 1.

Example 4

A thermal transfer sheet of Example 4 was obtained by carrying out thesame procedure as in Example 1 except that a coating liquid for colorantlayer 4 having the following composition was used in place of thecoating liquid for colorant layer 1.

<Coating Liquid for Colorant Layer 4>

C.I. Disperse Yellow 54 (it is referred to as “dye A”) 4.75 partsDispersant of acryl-based block type polymer 1.67 parts (solid content1.0 part) (BYK-LPN6919, weight average molecular weight: 9000, solidcontent: 60%, manufactured by BYK Additives & Instruments)Polyether-based dispersant 0.7 part (Solsperse 20000, weight averagemolecular weight: 1900, manufactured by The Lubrizol Corporation)Polyvinyl acetal resin 2.05 parts (KS-5, manufactured by SekisuiChemical Co., Ltd.) Methyl ethyl ketone 32.25 parts  Toluene 32.25parts 

The chemical formula of the dye A is that as mentioned above.

Example 5

A thermal transfer sheet of Example 5 was obtained by carrying out thesame procedure as in Example 1 except that a coating liquid for colorantlayer 5 having the following composition was used in place of thecoating liquid for colorant layer 1.

<Coating Liquid for Colorant Layer 5>

C.I. Disperse Yellow 54 (it is referred to as “dye A”) 4.275 partsPigment represented by the above Formula 3 0.475 parts (sulfonatedderivative of C.I. Pigment Yellow 138) Dispersant of acryl-based blocktype polymer  2.83 parts (solid content 1.7 parts) (BYK-LPN6919, weightaverage molecular weight: 9000, solid content: 60%, manufactured by BYKAdditives & Instruments) Polyvinyl acetal resin  2.05 parts (KS-5,manufactured by Sekisui Chemical Co., Ltd.) Methyl ethyl ketone 32.25parts Toluene 32.25 parts

The chemical formula of the dye A is that as mentioned above.

Example 6

A thermal transfer sheet of Example 6 was obtained by carrying out thesame procedure as in Example 1 except that a coating liquid for colorantlayer 5 having the following composition was used in place of thecoating liquid for colorant layer 1.

<Coating Liquid for Colorant Layer 6>

C.I. Disperse Yellow 54 (it is referred to as “dye A”) 9.00 partsPigment represented by the above Formula 3 0.90 parts (sulfonatedderivative of C.I. Pigment Yellow 138) Dispersant of acryl-based blocktype polymer 4.08 parts (solid content 2.45 parts) (BYK-LPN6919, weightaverage molecular weight: 9000, solid content: 60%, manufactured by BYKAdditives & Instruments) Polyvinyl acetal resin 3.50 parts (KS-5,manufactured by Sekisui Chemical Co., Ltd.) Methyl ethyl ketone 42.00parts  Toluene 42.00 parts 

The chemical formula of the dye A is that as mentioned above.

Example 7

A thermal transfer sheet of Example 7 was obtained by carrying out thesame procedure as in Example 1 except that a coating liquid for colorantlayer 7 wherein 4.25 parts (solid content: 1.7 parts) of an acryl-basedblock type polymer dispersant (BYK-LPN21116, weight average molecularweight: 8000, solid content: 40%, manufactured by BYK Additives &Instruments) was used instead of 2.83 parts (solid content: 1.7 parts)of an acryl-based block type polymer dispersant (BYK-LPN6919, weightaverage molecular weight: 9000, solid content: 60%, manufactured by BYKAdditives & Instruments) in the composition of the coating liquid forcolorant layer 5 was used in place of the coating liquid for colorantlayer 1.

Example 8

A thermal transfer sheet of Example 8 was obtained by carrying out thesame procedure as in Example 1 except that a coating liquid for colorantlayer 8 having the following composition was used in place of thecoating liquid for colorant layer 1.

(Preparation of Coating Liquid for Colorant Layer 8)

As the following composition, a dispersion was prepared by adding acolorant, a dispersant, a binder resin, a solvent and 250 parts byweight of zirconia beads having a particle diameter of 2.0 mm into aglass bottle, sealing the glass bottle, shaking the content with a paintshaker (manufactured by Asada Iron Works Co., Ltd.) for 1 hour as apreliminary crushing, then removing the above mentioned zirconia beadsfrom the bottle and adding 250 parts by weight of zirconia beads havinga particle diameter of 0.1 mm to the bottle, and dispersing the contentwith the paint shaker similarly for 3 hour as a main crushing, in orderto prepare the dispersion. Then, 50 parts of a binder solution havingthe following composition was added to 50 parts of thus prepareddispersion, in order to prepare a coating liquid for colorant layer 8.

<Dispersion>

C.I. Disperse Yellow 54 (“dye A”)  9.9 parts Azo-based dispersant  0.7part (Solsperse 22000, manufactured by The Lubrizol Corporation)Dispersant of urethane-based polymer 13.33 parts (solid content 4.0parts) (BYK-161, solid content: 30%, manufactured by BYK Additives &Instruments) Methyl ethyl ketone 32.25 parts Toluene 32.25 parts

The chemical formula of the dye A is that as mentioned above.

<Binder Solution>

Polyvinyl acetal resin 4.68 parts   (KS-5, manufactured by SekisuiChemical Co., Ltd.) Methyl ethyl ketone 50 parts Toluene 50 parts

Example 9

A thermal transfer sheet of Example 9 was obtained by carrying out thesame procedure as in Example 1 except that a coating liquid for colorantlayer 9 having the following composition was used in place of thecoating liquid for colorant layer 1.

(Preparation of Coating Liquid for Colorant Layer 9)

The same procedure for the preparation of the coating liquid forcolorant layer 10 was carried out except that 10.53 parts (solidcontent: 4.0 parts) of an urethane-based polymer dispersant (BYK-162,solid content: 38%, manufactured by BYK Additives & Instruments) wasused instead of 13.33 parts (solid content: 4.0 parts) of theurethane-based polymer dispersant (BYK-161, solid content: 30%,manufactured by BYK Additives & Instruments) in the dispersion used forpreparing the above mentioned coating liquid for colorant layer 8, inorder to prepare a coating liquid for colorant layer 9.

Example 10

A thermal transfer sheet of Example 10 was obtained by carrying out thesame procedure as in Example 1 except that a coating liquid for colorantlayer 10 having the following composition was used in place of thecoating liquid for colorant layer 1.

<Coating Liquid for Colorant Layer 10>

C.I. Disperse Yellow 201  2.0 parts C.I. Disperse Yellow 54 (“Dye A”) 4.0 parts Quinophthalone-based dye represented by the following  2.0parts formula 4 Pigment represented by the above Formula 3 0.42 parts(sulfonated derivative of C.I. Pigment Yellow 138) Dispersant ofacryl-based block type polymer 4.25 parts (solid content 1.7 parts)(BYK-LPN21116, weight average molecular weight: 8000, solid content:40%, manufactured by BYK Additives & Instruments) Polyvinyl acetal resin2.50 parts (KS-5, manufactured by Sekisui Chemical Co., Ltd.)Polyethylene wax (particle diameter: 5 μm) 0.09 parts Toluene   33 partsMethyl ethyl ketone   33 parts

The chemical formula of the dye A is that as mentioned above.

Comparative Example 1

As the following composition, a coating liquid for colorant layer A wasprepared by adding a colorant, a dispersant, a binder resin, a solventand 250 parts by weight of zirconia beads having a particle diameter of2.0 mm into a glass bottle, sealing the glass bottle, shaking thecontent with a paint shaker (manufactured by Asada Iron Works Co., Ltd.)for 1 hour as a preliminary crushing, then removing the above mentionedzirconia beads from the bottle and adding 250 parts by weight ofzirconia beads having a particle diameter of 0.1 mm to the bottle, anddispersing the content with the paint shaker similarly for 96 hour as amain crushing, in order to prepare a coating liquid for colorant layerA. The thermal transfer sheet of the Comparative example 1 was preparedby carrying out the same procedure as in Example 1 except that thecoating liquid for colorant layer A prepared by the following procedurewas used instead of the coating liquid for colorant layer 1.

<Coating Liquid for Colorant Layer A>

C.I. Disperse Yellow 54 (“dye A”)  4.75 parts Polyvinyl acetal resin 3.75 parts (KS-5, manufactured by Sekisui Chemical Co., Ltd.) Methylethyl ketone 32.25 parts Toluene 32.25 parts

The chemical formula of the dye A is that as mentioned above.

Comparative Example 2

A thermal transfer sheet of Comparative example 2 was obtained bycarrying out the same procedure as in Example 1 except that a coatingliquid for colorant layer B having the following composition was used inplace of the coating liquid for colorant layer 1. Incidentally, thecoating liquid for colorant layer B was the one which was prepared bydissolving a dye and a resin in a solvent. Ditto for a coating liquidfor colorant layer C.

<Coating Liquid for Colorant Layer B>

Quinophthalone-based dye represented by the  4.75 parts followingformula 4 Polyvinyl acetal resin  3.75 parts (KS-5, manufactured bySekisui Chemical Co., Ltd.) Methyl ethyl ketone 32.25 parts Toluene32.25 parts

Comparative Example 3

A thermal transfer sheet of Comparative example 3 was obtained bycarrying out the same procedure as in Example 1 except that a coatingliquid for colorant layer C having the following composition was used inplace of the coating liquid for colorant layer 1.

<Coating Liquid for Colorant Layer C>

C.I. Disperse Yellow 54 (“dye A”) 4.75 parts Polyvinyl acetal resin 3.75parts (KS-5, manufactured by Sekisui Chemical Co., Ltd.) Polyethylenewax (particle diameter: 5 μm) 0.99 parts Methyl ethyl ketone   33 partsToluene   33 parts

(Volume Average Particle Diameter of the Colorant)

With respect to the coating liquids for colorant layer 1-10, and A-C,which were prepared in the above Examples and Comparative examples formanufacturing thermal transfer sheet, the volume average particlediameter (nm) of colorant in each individual coating liquid which wasdispersed in accordance with the above mentioned colorant dispersingcondition was determined by using the particle size distributionmeasuring apparatus in accordance with the laser diffraction scatteringmethod as mentioned above. The obtained results are shown in Table 1.

(State of Coating Liquid)

With respect to the coating liquids for colorant layer which wereprepared in the above Examples and Comparative examples formanufacturing thermal transfer sheet, each coating liquid was observedvisually, at the initial time after preparing the coating liquid inaccordance with the above mentioned colorant dispersing condition, andafter being left for 120 hours at room temperature from the initialtime, about the presence or absence of precipitate in the coatingliquid. The evaluation was done according to the following criteria.

1: There was no precipitate at all.2: There was substantially no precipitate.3: There was a little precipitate.4; There was a lot of precipitate.

(Adhesiveness)

With respect to the thermal transfer sheets prepared as above, theadhesiveness of the colorant layer to the substrate sheet was examinedby applying a cellophane tape to a surface of the colorant layer,rubbing the applied cellophane tape with a thumb by a to-and-fro motionso as to attach the cellophane tape to the colorant layer, and peelingthe cellophane tape off from the colorant layer with an angle of 180° byhand just after the attaching. The evaluation was done by observingvisually the state of transition of the colorant layer onto thepeeled-off cellophane tape. Criteria for this evaluation are as follows.

1: The transition of the colorant layer onto the cellophane tape was notobserved at all.2: Although the transition of the colorant layer onto the cellophanetape was observed with a very little extent, but no problem arises in apractical use.3: Although the transition of the colorant layer onto the cellophanetape was observed with a little extent, but no problem arises in apractical use.4: The transition of the colorant layer onto the cellophane tape wasobserved with a certain extent.

(Printing Aptitude)

Using a test printer, and combining the each individual thermal transfersheet as mentioned above with a thermal transfer receiving sheetprepared in accordance with the following condition, under the followingprinting condition 1, a yellow gradation pattern was printed in order toexamine the density characteristics and the presence or absence of theabnormal transfer. The evaluation of the density characteristics wasdone at the highest concentration when applying a maximum energy and ata concentration of the highlight portion when applying a 60% energy. Themeasured concentrations are shown in Table 1. The evaluation of theabnormal transfer was done in accordance with the following criteria.

1: Abnormal transfer was not observed.2: Although it was within a level of no problem in the practical use, alittle stronger resisting level was observed on the peeling the thermaltransfer sheet off from the thermal transfer receiving sheet afterprinting.3: Abnormal transfer was observed.

(Printing Condition 1)

Thermal head: F3598 (manufactured by Toshiba Hokuto Electronics Co.,Ltd.)

Average resistance value of heating element: 5176 (Ω)

Printing density along the main scanning direction: 300 dpi

Printing density along the sub scanning direction: 300 dpi

Printing Power: 0.12 (W/dot)

1-line period: 2 (msec.)

Pulse duty: 85%

print-starting temperature: 35.5 (° C.)

(Preparation of Thermal Transfer Image-Receiving Sheet)

On a porous film layer made of a porous polyethylene film (Toyopearl-SSP4255, manufactured by Toyobo Co., Ltd., thickness: 35 μm), a coatingliquid for forming intermediate layer having the following composition,and a coating liquid for forming receiving layer having the followingcomposition, were coated and then dried in that order in accordance withthe gravure reverse coating method, in order to form an intermediatelayer and a receiving layer. On another side surface of the porouspolyethylene film which was opposite to the surface onto which theintermediate layer and the receiving layer were formed, a coating liquidfor forming adhesive layer having the following composition was coatedand then dried in accordance with the gravure reverse roll coatingmethod, in order to form an adhesive layer. Then, this adhesive layerside of the porous film was adhered to RC paper (155 g/m², 151 μm inthickness, manufactured by Mitsubishi Paper Mills) so as to form athermal transfer image-receiving sheet. With respect to the coatedamount of the above intermediate layer, receiving layer, and adhesivelayer were 1.5 g/m², 5.0 g/m², and 5.0 g/m² in a dried state,respectively.

<Coating Liquid for Intermediate Layer>

Polyester resin 50 parts (Polyester WR-905, manufactured by The NipponSynthetic Chemical Industry Co., Ltd.) Titanium oxide 20 parts (TCA888,manufactured by Tochem Products) Fluorescent whitening agent 1.2 parts(Uvitex BAC, manufactured by Ciba Specialty Chemicals Inc.)Water/isopropyl alcohol = 1/1 28.8 parts

<Coating Liquid for Receiving Layer>

Vinyl chloride-vinyl acetate copolymer 60 parts (SOLBIN C, manufacturedby Nissin Chemical Industry Co., Ltd.)) Epoxy-modified silicone 1.2parts (X-22-3000T, manufactured by Shin-Etsu Chemical Co., Ltd.)Metylstyl-modified silicone 0.6 parts (X-24-510, manufactured byShin-Etsu Chemical Co., Ltd.) Methyl ethyl ketone/toluene (mass ratio1:1) 5 parts

<Coating Liquid for Adhesive Layer>

Urethane resin  30 parts (TAKELAC A-969V, manufactured by Mitsui TakedaChemical Inc.) Isocyanate  10 parts (TAKENATE, manufactured by MitsuiTakeda Chemical Inc.) Ethyl acetate 100 parts

(Evaluation of Light Resistance)

The colorant layer of each individual thermal transfer sheet was opposedto the receiving layer surface of the thermal transfer image-receivingsheet and superposed thereon, and then they were subjected to printingby using the test printer from the backside of the thermal transfersheet under the above mentioned printing condition 1 so as to form ayellow printing pattern having 18 steps' gradation patterns of from0/255 to 255/255 (Max concentration). Furthermore, by using theprotective layer transfer sheet prepared in the following condition, andunder the following printing conditions 2, the transferable protectivelayer was transferred onto the yellow printing pattern in order toobtain a final printed article.

(Preparation of Protective Layer Transfer Sheet)

As a substrate, polyethylene terephthalate (PET) film which had 4.5 μmin thickness was used. On a surface of this substrate, a coating liquidfor peeling layer having the following composition was coated so as toobtain a coating amount of solid content of 1.0 g/m² in accordance withthe wire bar coating method, and then the coated liquid was dried on anoven at 110° C. for 1 minute to form a peeling layer. Then, on thepeeling layer, the above mentioned coating liquid for primer layer whichwas used in the above mentioned preparation of the thermal transfersheet was coated so as to obtain a coating amount of solid content of0.2 g/m² in accordance with the wire bar coating method, and then thecoated liquid was dried on the oven at 110° C. for 1 minute to form aprimer layer. Next, on the primer layer, a coating liquid for adhesivelayer mentioned below was coated so as to obtain a coating amount ofsolid content of 1.0 g/m² in accordance with the wire bar coatingmethod, and then the coated liquid was dried on the oven at 110° C. for1 minute to form an adhesive layer. Incidentally, on another surface ofthis substrate, the coating liquid for back face layer 1 which had theabove mentioned composition and which was used in the above mentionedpreparation of the thermal transfer sheet was coated so as to obtain acoating amount of solid content of 1.0 g/m² and then the coated liquidwas dried to form a back face layer in advance. Ultimately, a protectivelayer transfer sheet wherein the peeling layer, the primer layer and theadhesive layer which constituted the transferable protective layer werelayered in this order on one surface of the substrate sheet, and theback face layer was provided on the another surface of the substrate wasobtained.

<Coating Liquid for Peeling Layer>

Polymethyl methacrylic acid (PMMA) 20 parts (Dianal BR-87, manufacturedby Mitsubishi Rayon Co., Ltd.) Toluene 40 parts Methyl ethyl ketone 40parts

<Coating Liquid for Adhesive Layer>

Polyester resin 23.5 parts (VYLON 220, manufactured by Toyobo Co., Ltd.)UVA compound 6 parts (Tinuvin 900, manufactured by Ciba SpecialtyChemicals Co., Ltd.) Silica filler 25 parts (Sylysia 310P, manufacturedby FUJI Silysia Chemical Ltd.) Toluene 35 parts Methyl ethyl ketone 35parts

(Printing Condition 2)

Thermal head: F3598 (manufactured by Toshiba Hokuto Electronics Co.,Ltd.)

Average resistance value of heating element: 5176 (Ω)

Printing density along the main scanning direction: 300 dpi

Printing density along the sub scanning direction: 300 dpi

Printing Power: 0.096 (W/dot)

1-line period: 2 (msec.)

Pulse duty: 85%

print-starting temperature: 35.5 (° C.)

The yellow printing pattern of the final printed article obtained by theabove procedure underwent light irradiation under the followingcondition.

(Irradiation Conditions)

Irradiation tester: Ci35 manufactured by Atlas Corp.

Light source: xenon lamp

Filter: inside=IR filter, outside=soda lime glass

Black panel temperature: 45° C.

Irradiation intensity: 1.2 W/m², measured at 420 nm

Irradiation energy: 700 kJ/m², integrated value at 420 nm

The color difference of images before and after the irradiation of theabove irradiation condition was measured by a spectrophotometer(SpectroLino, manufactured by Gretag Macbeth Co., Ltd.). The measurementresults are shown in Table 1. With respect to this measurement, themeasurement was carried out for the places where the OD of Ye (yellowprinted portion) before irradiation was at around 1.0.

Color difference ΔE* ^(ab)=((Δa*)²+(Δb*)²)^(1/2)

Please see, CIE 1976 La* b* color system (JIS Z8729 (1980))

Δa*=a*(after irradiation)−a*(before irradiation)

Δb*=b*(after irradiation)−b*(before irradiation)

Incidentally, a* and b* are based on the CIE 1976 L* A* b* color system,and the a* and b* represent perceptual brightness indexes.

(Contamination to the Back Face Layer)

The contamination to the back layer was evaluated in order to determinethe storage stability of the thermal transfer sheet. The prepared dyeface was opposed to the surface of the back face layer of the followingsubstrate having the back face layer and superposed thereon, and thenthey were stored for 98 hours under loading of 40 kg/m² at 40° C., 90%RH, in order to evaluate the migration of colorant to the back facelayer. For this evaluation of migration, the surfaces of the back facelayers before and after the storage were measured by thespectrophotometer (SpectroLino, manufactured by Gretag Macbeth Co.,Ltd.), and then, the color difference (ΔE*^(ab)) was calculated inaccordance with the following equation. The obtained results are shownin Table 1. Here, the above mentioned substrate having the back facelayer was the one which was obtained by coating the coating liquid forback face layer 1 which had the above mentioned composition and whichwas used in the above mentioned preparation of the thermal transfersheet, on a polyethylene terephthalate (PET) film which had 4.5 μm inthickness, so as to obtain a coating amount of solid content of 1.0 g/m²in accordance with the wire bar coating method, and then drying thecoating liquid so as to form the back face layer.

Color difference ΔE* ^(ab)=((Δa*)²+(Δb*)²)^(1/2)

Please see, CIE 1976 La* b* color system (JIS Z8729 (1980))

Δa*=a*(after storage)−a*(before storage)

Δb*=b*(after storage)−b*(before storage)

Incidentally, a* and b* are based on the CIE 1976 L* A* b* color system,and the a* and b* represent perceptual brightness indexes.

Here, the smaller the value of the ΔE*^(ab) becomes, the lesscontamination arises. In other words, it indicates that the degree ofkick is less.

The respective results of the above evaluations are shown in Table 1.

TABLE 1 Density Density Volume average characteristics characteristicsLight resistance particle State of Adhe- Abnormal (Density at the(Density at 60% color difference Contamination diameter (nm) coatingliquid siveness transfer maximum energy) energy) (ΔE*^(ab)) (ΔE*^(ab))Example 1 258 2 1 1 2.32 0.5 8 0.8 Example 2 265.7 2 1 1 2.31 0.51 8 0.9Example 3 249.3 2 1 1 2.33 0.51 8 0.8 Example 4 267.6 2 1 1 2.31 0.51 80.9 Example 5 193.1 2 1 1 2.34 0.53 8 0.8 Example 6 195.2 2 2 2 2.570.55 8 1.2 Example 7 182.5 2 1 1 2.35 0.52 8 0.8 Example 8 158.9 2 1 12.34 0.54 8 1.3 Example 9 161.4 2 1 1 2.33 0.54 8 1.5 Example 10 189.5 21 2 2.70 1.05 10 4 Comparative 494.4 4 3 3 2.27 0.39 9 1 Example 1Comparative — 1 1 1 2.18 0.99 8 10.9 Example 2 Comparative — 1 3 2 2.481.13 14 12.2 Example 3

As shown above, with respect to the coating liquids for colorant layer1-10 which were used for preparing the thermal transfer sheets ofExamples 1 to 10, the volume average particle diameters of all colorantswere in the range of less than 270 nm and the colorants were uniformlydispersed, and there was substantially no precipitate, and thus theybrought no problem in practical use as the coating liquid. In addition,there was also no problem in the adhesiveness. Furthermore, with respectto the printed articles that were formed using the thermal transfersheets of Examples 1-10, no abnormal transfer was observed, and thedensity was also excellent as indicating 2.3 at the maximum density.Further, the light resistance was also good. Further, the colorantcontamination to the back face layer was also in low level, thus thestorage stability of the thermal transfer sheet was good. In particular,with respect to the coating liquids for colorant layer 7-10 which wereused for preparing the thermal transfer sheets of Examples 1 to 7, thevolume average particle diameters of colorants were miniaturized to 190nm or less, and the density at the 60% energy and the density at themaximum energy were in relatively high level. In addition, with respectto the thermal transfer sheets of Examples 7-10 which have the colorantlayer formed by using each individual coating liquids for colorant layer7-10, the colorant contamination to the back face layer was also in lowlevel, thus the storage stability of the thermal transfer sheet wasgood.

In particular, with respect to the coating liquids for colorant layerthat were prepared in accordance with the above mentioned “thirdprocedure for preparation of the coating liquid for colorant layer”,that is, the coating liquids for colorant layer 8 and 9, which wereprepared by post-addition of a liquid containing a binder resin, it waspossible to miniaturize the particle diameter with a short period'sdispersion (3 hours' dispersion for the coating liquids for colorantlayer 8 and 9, whereas, 24 hours' dispersion for the coating liquids forcolorant layer 1-7, and 10)

Further, with respect to the thermal transfer sheet of Example 10 whichwas prepared by using the coating liquid for colorant layer 10 whichcontained the colorant that was dispersible in the solvent, and theother colorant that was soluble in the solvent, it was possible toheighten the density at the 60% energy and the density at the maximumdensity, and also to obtain a good light resistance and a good storagestability.

In contrast, the printed article that was formed by using the thermaltransfer sheet of Comparative Example 1 suffered with an inferior resultin the highlight density and the abnormal transfer observed. The coatingliquid for colorant layer A which was used for forming the thermaltransfer sheet of Comparative Example 1 had a volume average particlediameter of the colorant of more than 300 nm, and tended to causeprecipitation of the colorant, and thus, owned problems in the practicaluse. Also, the thermal transfer sheet of Comparative Example 1 possesseda low adhesiveness, and thus, owned problems in the practical use. Thethermal transfer sheets of Comparative Examples 2 and 3 suffered withinferior results in the colorant contamination to the back face layer.

Example 11

As a substrate, polyethylene terephthalate film which underwenteasy-adhesive treatment in advance, and has 4.5 μm in thickness wasused. On one surface of this substrate, a coating liquid for back facelayer 2 having the following composition was coated so as to obtain acoating amount of solid content of 0.5 g/m² and then the coated liquidwas dried to form a back face layer. Then, on another surface of thesubstrate, the coating liquid for primer layer having the abovementioned composition was coated so as to obtain a coating amount ofsolid content of 0.1 g/m² and then the coated liquid was dried to formthe primer layer. Next, on the primer layer, a coating liquid forcolorant layer 11 which was prepared in accordance with the procedurementioned below was coated so as to obtain a coating amount of solidcontent of 1.0 g/m², and then the coated liquid was dried to form ancolorant layer. Ultimately, a thermal transfer sheet of Example 11 wasprepared.

<Coating Liquid for Back Face Layer 2>

Polyvinyl acetal resin 60.8 parts (S-LEC BX-1, manufactured by SekisuiChemical Co., Ltd.) Polyisocyanate 4.2 parts (BURNOCK D750, manufacturedby DIC Corporation) Zinc stearyl phosphate 10 parts (LBT-1830 purified,manufactured by Sakai Chemical Industry Co., Ltd.) Zinc stearate 10parts (SZ-PF, manufactured by Sakai Chemical Industry Co., Ltd.) Talc 5part (MICRO ACE P-3, manufactured by Nippon Talc Co., Ltd.) Polyethylenewax 10 parts (Polyethylene wax 3000, manufactured by Toyo ADLCorporation) toluene 200 parts methyl ethyl ketone 100 parts

(Preparation of Coating Liquid for Colorant Layer 11)

A coating liquid for colorant layer 11 was prepared by adding acolorant, a dispersant, a binder resin, a polyethylene wax, and asolvent as the following composition of a coating liquid for colorantlayer 11, as well as 250 parts by weight of zirconia beads having aparticle diameter of 2.0 mm into a glass bottle, sealing the glassbottle, shaking the content with a paint shaker (manufactured by AsadaIron Works Co., Ltd.) for 1 hour as a preliminary crushing, thenremoving the above mentioned zirconia beads from the bottle and adding250 parts by weight of zirconia beads having a particle diameter of 0.1mm to the bottle, and dispersing the content with the paint shakersimilarly for 24 hour as a main crushing.

<Coating Liquid for Colorant Layer 11>

C.I. Disperse Yellow 201  2.3 parts C.I. Disperse Yellow 54  2.3 partsPigment represented by the above Formula 3 0.42 parts (sulfonatedderivative of C.I. Pigment Yellow 138) Dispersant of acryl-based blocktype polymer 4.25 parts (solid content 1.7 parts) (BYK-LPN21116, weightaverage molecular weight: 8000, solid content: 40%, manufactured by BYKAdditives & Instruments) Polyvinyl acetal resin 2.05 parts (KS-5,manufactured by Sekisui Chemical Co., Ltd.) Polyethylene wax (particlediameter: 5 μm) 0.09 part  Toluene   33 parts Methyl ethyl ketone   33parts

Example 12

A thermal transfer sheet of Example 12 which was provided with acolorant layer wherein a first colorant layer and a second colorantlayer were layered was obtained by carrying out the same procedure as inExample 11 except that a coating liquid for colorant layer 12 having thefollowing composition was coated on the substrate sheet so as to obtaina coating amount of solid content of 0.5 g/m² and then the coated liquidwas dried to form the first colorant layer, and then a coating liquidfor colorant layer 13 having the following composition was coated on thefirst colorant layer so as to obtain a coating amount of solid contentof 0.5 g/m² and then the coated liquid was dried to form the secondcolorant layer, instead of using the coating liquid for colorant layer11 of Example 11. Incidentally, the coating liquid for colorant layer 13was prepared by a manufacturing procedure similar to that for the abovementioned coating liquid for colorant layer 11.

(Preparation of Coating Liquid for Colorant Layer 12)

A coating liquid for colorant layer 12 was prepared by adding acolorant, a dispersant, a binder resin, a polyethylene wax, and asolvent as the following composition of a coating liquid for colorantlayer 12 into a glass bottle, sealing the glass bottle, heating thecontent at 50° C. for 1 hour, and then shaking the heated content with apaint shaker (manufactured by Asada Iron Works Co., Ltd.) for 30minutes.

<Coating Liquid for Colorant Layer 12>

C.I. Disperse Yellow 201 3.51 parts Polyvinyl acetal resin 2.63 parts(KS-5, manufactured by Sekisui Chemical Co., Ltd.) Polyethylene wax(particle diameter: 5 μm) 0.06 part  Toluene   33 parts Methyl ethylketone   33 parts

<Coating Liquid for Colorant Layer 13>

C.I. Disperse Yellow 54 3.31 parts Pigment represented by the aboveFormula 3 0.20 parts (sulfonated derivative of C.I. Pigment Yellow 138)Dispersant of acryl-based block type polymer 2.975 parts  (solid content1.19 parts) (BYK-LPN21116, weight average molecular weight: 8000, solidcontent: 40%, manufactured by BYK Additives & Instruments) Polyvinylacetal resin 1.44 parts (KS-5, manufactured by Sekisui Chemical Co.,Ltd.) Toluene   33 parts Methyl ethyl ketone   33 parts

Example 13

A thermal transfer sheet of Example 13 was obtained by carrying out thesame procedure as in Example 11 except that a coating liquid forcolorant layer 14 wherein a sublimable dye represented by the followingformula 5 (2.3 parts) was used instead of the C. I. Disperse Yellow 201(2.3 parts) in the coating liquid for colorant layer 11 was used inplace of the coating liquid for colorant layer 11.

Comparative Example 4

A thermal transfer sheet of Comparative example 4 was obtained bycarrying out the same procedure as in Example 11 except that the coatingliquid for colorant layer 12 having the above mentioned composition wasused in place of the coating liquid for colorant layer 11, and thecoating liquid for colorant layer 12 was coated so as to obtain acoating amount of solid content of 1.0 g/m² and then the coated liquidwas dried.

Comparative Example 5

A thermal transfer sheet of Comparative example 5 was obtained bycarrying out the same procedure as in Example 11 except that a coatingliquid for colorant layer D wherein a sublimable dye represented by thefollowing formula 5 (3.51 parts) was used instead of the C. I. DisperseYellow 201 (3.51 parts) in the coating liquid for colorant layer 12 wasprepared and the coating liquid for colorant layer D was coated so as toobtain a coating amount of solid content of 1.0 g/m² and then the coatedliquid was dried. Incidentally, the coating liquid for colorant layer Dwas prepared by a manufacturing procedure similar to that for the abovementioned coating liquid for colorant layer 12.

(Evaluation of Printing Density)

Using the same test printer that was used in the evaluation of theprinting aptitude, and combining each individual thermal transfer sheetof Examples and Comparative Examples with the thermal transferimage-receiving sheet prepared in the above conditions, the gradationpattern was printed under the above mentioned printing condition 1 toexamine the density property. The density property was measured at thehighest density when applying a maximum energy, the evaluation of printdensity was done in accordance with the following criteria. Thereflection density was measured by the spectrometer (SpectroLino,manufactured by Gretag Macbeth Co., Ltd.). The evaluation results areshown in Table 2.

“Evaluation criteria”⊚: Concentration was not less than 2.1.∘: Concentration was not less than 2.0 and less than 2.1.Δ: Concentration was less than 2.0.

(Evaluation of Contamination)

The contamination to the back layer was evaluated in order to determinethe storage stability of the thermal transfer sheet. The evaluation ofcontamination was carried out in the same method as the above mentionedevaluation of the contamination to the back surface layer of Examples1-10 and Comparative Examples 1-3, and the evaluation of contaminationwas done in accordance with the following criteria. The evaluationresults are shown in Table 2.

“Evaluation criteria”α: ΔE*^(ab) was less than 10.Δ: ΔE*^(ab) was not less than 10.

(Scumming Evaluation)

The scumming of the printed article was evaluated in order to determinethe storage stability of the thermal transfer sheet. In order toevaluate the scumming, a group wherein each individual thermal transfersheet of Examples and Comparative examples had been stored for 60 hoursunder a condition of 50° C. and 80% RH, and another group wherein eachindividual thermal transfer sheet of Examples and Comparative exampleshad not been stored in such a condition as above mentioned wereprepared. Then, using predetermined image-receiving paper, the printingwas executed. The white background portion of each individual printedarticle obtained, to which no energy had been applied, underwentmeasurement by using the spectrometer (SpectroLino, manufactured byGretag Macbeth Co., Ltd.), and the color difference (ΔE*^(ab)) wasdetermined by the following equation. Then, the scumming was evaluatedin accordance with the following criteria. The evaluation results arealso shown in Table 2.

Color difference ΔE* ^(ab)=((Δa*)²+(Δb*)²)^(1/2)

Please see, CIE 1976 La* b* color system (JIS Z8729 (1980))

Δa*=a*(after storage)−a*(before storage)

Δb*=b*(after storage)−b*(before storage)

Incidentally, a* and b* are based on the CIE 1976 L* A* b* color system,and the a* and b* represent perceptual brightness indexes.

Here, the smaller the value of the ΔE*^(ab) becomes, the less reductionunder high temperature and high humidity condition and the higherstoring stability arise.

“Evaluation criteria”⊚: ΔE*^(ab) was less than 0.2.∘: ΔE*^(ab) was not less than 0.2 and less than 0.3.Δ: ΔE*^(ab) was not less than 0.3.

TABLE 2 Printing Contamination Scrumming density evaluation evaluationExample 11 ◯ ◯ ◯ Example 12 ◯ ◯ ⊚ Example 13 ⊚ ◯ ◯ Comparative ◯ Δ Δexample 4 Comparative ⊚ Δ Δ example 5

As is apparent from Table 2, with respect to the printed articlesobtained by using the thermal transfer sheets of Examples 11 to 13, theconcentration was good as indicating a value of not less than 2.0 at thehighest concentration. In addition, the colorant contamination to theback face layer surface was in low level and the scumming was also inlow level, and thus the storage stability of the thermal transfer sheetwas good. In contrast, with respect to the printed articles obtained byusing the thermal transfer sheets of Comparative Examples 4 and 5,although the concentration was good enough, the colorant contaminationto the back face layer and the scumming increased, and thus the storagestability of the thermal transfer sheet became worse.

EXPLANATION OF NUMERALS

-   1 . . . thermal transfer sheet-   2 . . . substrate sheet-   3 . . . colorant layer-   4 . . . primer layer-   5 . . . back face layer-   10 y . . . sublimable dye capable of being dissolved in the    predetermined solvent-   10 x . . . colorant capable of being dispersed in the predetermined    solvent-   1X . . . thermal transfer sheet for comparison

1. A thermal transfer sheet comprising: a substrate and a colorant layer provided on one surface of the substrate sheet, the colorant layer containing a solvent as trace, a colorant dispersible in the solvent, a dispersant and a binder resin; wherein the dispersant being selected from the group consisting of polyether-based dispersants, graft type polymer dispersants, acryl-based block type polymer dispersants, urethane-based polymer dispersants and azo-based dispersants.
 2. Thermal transfer sheet according to claim 1, wherein the colorant comprises a quinophthalone-based colorant represented by the following formula 1:

Wherein, X represents a hydrogen atom or a halogen atom, R¹ represents a hydrogen atom, an alkyl group or derivative thereof having 1 to 5 carbon atoms, an acyl group including an alkyl group or a benzoic ring and having a total carbon number of 6 to
 10. 3. Thermal transfer sheet according to claim 2, wherein the colorant layer further contains another colorant represented by the following formula 2:

wherein, each of R¹-R⁵ represents independently a hydrogen atom, or a sulfonated derivative having at least one sulfonic acid group (—SO₃H) or sulfonamide group.
 4. A coating liquid for colorant layer of a thermal transfer sheet, comprising: a solvent, a colorant dispersible in the solvent, a dispersant and a binder resin; the colorant being dispersed in a particle size of not less than 50 nm and not more than 300 nm in the coating liquid; and, the dispersant being selected from the group consisting of polyether-based dispersants, graft type polymer dispersants, acryl-based block type polymer dispersants, urethane-based polymer dispersants and azo-based dispersants.
 5. The coating liquid for colorant layer according to claim 4, wherein the colorant comprises a quinophthalone-based colorant represented by the following formula 1

Wherein, X represents a hydrogen atom or a halogen atom, R¹ represents a hydrogen atom, an alkyl group or derivative thereof having 1 to 5 carbon atoms, an acyl group including an alkyl group or a benzoic ring and having a total carbon number of 6 to
 10. 6. A method of manufacturing a thermal transfer sheet, comprising: a colorant layer forming step of applying a coating liquid for colorant layer onto a surface of a substrate sheet; the coating liquid comprising a solvent, a colorant dispersible in the solvent, a dispersant and a binder resin; the colorant being dispersed in a particle size of not less than 50 nm and not more than 300 nm in the coating liquid; and, the dispersant being selected from the group consisting of polyether-based dispersants, graft type polymer dispersants, acryl-based block type polymer dispersants, urethane-based polymer dispersants and azo-based dispersants.
 7. The method of manufacturing a thermal transfer sheet according to claim 6, wherein the colorant comprises a quinophthalone-based colorant represented by the following formula 1:

Wherein, X represents a hydrogen atom or a halogen atom, R¹ represents a hydrogen atom, an alkyl group or derivative thereof having 1 to 5 carbon atoms, an acyl group including an alkyl group or a benzoic ring and having a total carbon number of 6 to
 10. 8. An image forming method for forming image on a thermal transfer image-receiving sheet comprising: using a thermal transfer sheet having a colorant layer on a surface of a substrate sheet in combination with the thermal transfer image-receiving sheet having a receiving layer on a surface of another substrate sheet, the colorant layer of the thermal transfer sheet containing a solvent as trace, a colorant dispersible in the solvent, a dispersant and a binder resin; and the dispersant being selected from the group consisting of polyether-based dispersants, graft type polymer dispersants, acryl-based block type polymer dispersants, urethane-based polymer dispersants and azo-based dispersants.
 9. The image forming method according to claim 8, wherein the colorant comprises a quinophthalone-based colorant represented by the following formula 1:

Wherein, X represents a hydrogen atom or a halogen atom, R¹ represents a hydrogen atom, an alkyl group or derivative thereof having 1 to 5 carbon atoms, an acyl group including an alkyl group or a benzoic ring and having a total carbon number of 6 to
 10. 10. A thermal transfer sheet comprising: a substrate and a colorant layer provided on one surface of the substrate sheet, the colorant layer containing a solvent as trace, a sublimable dye soluble in the solvent, a colorant dispersible in the solvent, and a binder resin.
 11. A thermal transfer sheet comprising: a substrate, a first colorant layer, and a second colorant layer, layered in this order; the first colorant layer containing a first solvent as trace, a sublimable dye soluble in the first solvent, and a first binder resin; and the second colorant layer containing a second solvent as trace, a colorant dispersible in the second solvent, and a second binder resin.
 12. A method of manufacturing a thermal transfer sheet, comprising: a colorant layer forming step of applying a coating liquid for colorant layer onto a surface of a substrate sheet; the coating liquid for colorant layer containing a solvent, a sublimable dye soluble in the solvent, a colorant dispersible in the solvent, and a binder resin.
 13. The method of manufacturing a thermal transfer sheet according to claim 12, wherein the coating liquid for colorant layer further contains a dispersant.
 14. A method of manufacturing a thermal transfer sheet, comprising: a first colorant layer forming step of applying a coating liquid containing a first solvent, a sublimable dye soluble in the first solvent and a first binder resin, onto a surface of a substrate sheet to form a first colorant layer; and a second colorant layer forming step of applying a coating liquid which contains a second solvent, a colorant dispersible in the second solvent and a second binder resin, onto the first colorant layer to form a second colorant layer. 